JPH026614A - Production of silicon carbide fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having high tensile strength in high yield of ceramics by spinning a silicon-containing polymeric compound having a specific recurring unit, contacting the obtained fiber with a nitrogen-containing compound having N-H bond to effect the infusibilization of the fiber and calcining the product at high temperature in vacuum, etc. CONSTITUTION:The objective silicon carbide fiber is produced by spinning a silicon-containing polymeric compound having the recurring structural unit of formula (n is 0 or positive integer of 1-10; R1 is H, alkyl or aryl; R2 is alkylene or phenylene) (e.g., butenylsilane polymer), contacting the obtained fiber with a nitrogen-containing compound having at least one N-H bond in a molecule (e.g., n-propylamine) to effect the infusibilization of the fiber and calcining the product in vacuum or in an inert gas atmosphere at 800-2000 deg.C.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention involves spinning a specific polyolefin (silicon-containing polymer compound) containing a SiH:+ group in the side chain, and then firing it at a high temperature. , relates to a method of manufacturing silicon carbide fibers.

[Conventional technology]

In recent years, the state of technological development of high-performance fibers, especially inorganic fibers, has been remarkable. For example, silicon carbide fibers, Si-Ti
-C-0 fibers, silicon nitride fibers, carbon fibers, glass fibers, SiO□-Ti02 fibers, etc. have been developed.

Some of them are already commercially available, and demand is expected to grow significantly in the future as high-strength fibers with excellent heat resistance, especially as reinforcing materials for basic materials such as resins, metals, and ceramics.

Among these, silicon carbide fiber, which is the object of the present invention, is particularly expected to be used as an advanced composite material due to its high-temperature properties. Some products are manufactured as "Nicalon" (Japanese Patent Publication No. 57-26527, Japanese Patent Publication No. 57-53892, Japanese Patent Publication No. 57-38548). This is produced according to the following formulas (I), (II), and (I[[) using dimethyldichlorosilane obtained by a direct method as a starting material.

+2nNaC1 (1) The step (1) is usually carried out by melting metallic sodium in xylene and dispersing it (at ~100°C), but the treatment of unreacted residual sodium is complicated. In addition, the step (II) is carried out under high temperature and high pressure (approximately 50
The reaction is carried out using a reaction accelerator such as 0° C. 1100 atm) or polyporosiloxane (350° C. 1 normal pressure), but those with low molecular weights cannot be used and the yield is low (50% or less). In step (I[), after melting or dry spinning, the target SiC fiber is obtained by infusibility treatment in air and then firing at 1200 to 1300'C in nitrogen or vacuum. Obtained SiC
Fibers contain free carbon (10 to 2 Qwt%) or silica (approximately 20 ivt%), which are said to have an adverse effect on product properties, particularly strength at high temperatures.

The purpose of the present invention is to solve the above-mentioned problems of the conventional method (i.e. (
1) The manufacturing process is complicated, (2) The yield is low, and (3) Free carbon or silica is included in the final SiC fiber It is about providing law.

[Means and effects for solving the problems] The present inventors have completed the present invention as a result of intensive studies to solve the problems of the above-mentioned conventional methods.

That is, the present invention has the following formula: (1) General formula (1) %Formula% (where n is 0 or a positive integer from 1 to 10, R1 is hydrogen, an alkyl group or an aryl group, and R2 is an alkylene group or a phenylene group) ) A silicon-containing polymer compound containing a repeating structural unit represented by the formula is spun into a fiber, and (2) the fiber is brought into contact with a nitrogen-containing compound containing at least one N-H bond in the molecule. and (3) further heating the infusible fiber at 800 to 2000° C. in vacuum or in an inert gas.

The present invention will be explained in detail below.

The polymer used as a starting material in the present invention is a carbon-based polymer containing a silyl group (SiH3 group) in the side chain, and is a silicon-containing polymer containing a repeating structural unit represented by the general formula (1). It is a molecular compound, and this is the most significant feature of the present invention.

The degree of polymerization m of the polymer compound formed by formula (1) is 3 or more,
Preferably it is 10 or more, more preferably 50 or more.

Further, n is O or a positive integer from 1 to 1o, and from the viewpoint of ceramic yield (Si weight in fired body/Si weight in silicon-containing polymer compound (%)), the smaller the value, the more preferable it is. is O. R3 is hydrogen, an alkyl group, or an aryl group, such as -H, -CH3, -
Examples include C2H5, l-C3H7, -Φ (-Φ represents a phenyl group. The same applies hereinafter), Φ-C13, -CH2-Φ, etc., and those with fewer carbon atoms are more preferable, and hydrogen is most preferable. R2 is an alkylene group or a phenylene group, such as -CH2-, CH2?21IC)+2TE4, -ΦCH2-Φ-, and like R1, the smaller the number of carbon atoms, the more preferable it is. In addition, the above R0 and R2 are -COO
It may contain functional groups such as II, NO3--OH, etc.

Further, it may be either chain-like or cyclic, and in the case of a chain-like structure, the terminal thereof is hydrogen, an alkyl group, or the like.

Further, the silicon-containing polymer compound in the present invention may be a polymer consisting only of the same type of repeating structural units represented by the general formula (1), or may be a polymer consisting only of the same type of repeating structural units represented by the general formula (1). It may also be a polymer consisting of different types of repeating structural units. Of course, there is no limit to the stereoregularity of these polymers, and they may have any stereostructure, such as isotactic, syndiotactic, or actuctic. This molecular weight is not particularly limited, but is usually 100 to 10,000,000, preferably 200 to 1.0
00,000 is desirable in terms of ease of processing and solubility in solvents.

In addition, the repeating structural unit and other vinyl polymer structures that do not contain silicon, such as ethylene, propylene,
It may also be a copolymer consisting of repeating structural units derived from vinyl such as styrene, vinyl chloride, butene, isobutyne, HMA, etc. Such copolymerization may be random, alternating, block, or graft. In this case, the content of the structural unit of the present invention is preferably at least 0.1% by weight. The molecular weight of these copolymers is not particularly limited, but is usually 100 to io, oo
o, ooo, preferably 200 to 1,000.000
It is desirable to have a certain degree of ease of processing and solubility in solvents.

Needless to say, it is particularly desirable for the silicon-containing polymer compound used in the present invention to be easily processable and to have a high ceramic yield for the purpose of the present invention. Ease of manufacturing, meltability, and solvent solubility (processability) of the polymer
As a particularly preferable example, the repeating structural unit is -←CH2-C11→-1-←C1h-CH→
Examples include silicon-containing polymer compounds containing one or more of -5iH:+ (AlzSiH:+ or -←CH2-CH→- CHzCHzSiH3) and copolymers thereof.

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

For example, a method in which an α-olefin having a SiH group is subjected to coordination anionic polymerization using a Ziegler-Natta type catalyst (a transition metal salt such as a titanium halide, a vanadium halide, a zirconium halide, and an alkyl aluminum); Metal oxide (C
r03.5i02, Al2O3, etc.), hydrogen acid (H2SO
4, H3P0. , HCl0n, HCI, etc.), cationic polymerization using Lewis acid (BFa, AlC41, FeC1z, 5nC1, etc.) catalysts, alkali metal (
Li, Na, K, etc.), alkyl alkali (CzHsN
A, (CzHs)+AI, C6H5Li, etc.), an anionic polymerization method using a hydroxide (NaOI+, KOH, etc.) catalyst, and a radical polymerization method using a peroxide as an initiator. Naturally, polymerization can be carried out in either gas phase or liquid phase, and in a solvent or without a solvent (bulk polymerization). Furthermore, in these polymerizations, the molecular weight of the polymer can be easily adjusted by coexisting hydrogen or the like.

The α-olefin containing a 5ino group, which is a monomer for polymerization, can be produced by various methods, and is not particularly limited in the present invention, but for example, a method as shown in the following formula can be adopted.

1cI H5iCh+CIHzC-(CHz), -CH=CHz
600'C CI -olefin can be obtained (Japanese Patent Application No. 620888)
71, patent application No. 62-089888). Cover and 5iHi
In recent years, demand for use in polysilicon and amorphous silicon has expanded, and it has become possible to produce it cheaply and in large quantities, and it is a new silicon raw material that is expected to continue to grow in this trend. Therefore, SiH in the present invention
, l group-containing silicon-containing polymer compound has this 5iH
It can be said that it has great significance in that it can be easily and inexpensively produced by polymerizing a monomer obtained from a and an olefin. In addition, the polymer of the present invention when using this SiH4 is as described in the above-mentioned prior art section. ■, ■, and ■ use 5iHa as a raw material, and in particular, ■ and ■ are hydrosilylation reactions that use group II metals as catalysts, and compared to the target α, their production is carried out in a non-chlorine system. There is no fear of corrosion and the process is extremely simple. From the above, it is believed that the polymer according to the present invention will be able to be manufactured at even lower cost in the future.

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

Fiberization of the silicon-containing polymer compound in the present invention can be carried out basically in the same manner as in the case of using a conventional prepolymer having repeating structural units such as polycarbosilane.

That is, taking advantage of the easy processability of the silicon-containing polymer compound of the present invention, it is spun by any of melting, wet or dry spinning methods in an inert gas, particularly preferably by melting or dry spinning methods. .

Next, a method of infusible treatment of the obtained fibers with a nitrogen-containing compound will be described. The nitrogen-containing compound in the present invention is one having at least one N-H bond in the molecule, specifically NH3, NHzNHz, CHJH.
z, C2H3NH2, CHz=CH-CHzNHz,
(CHs)zNH, CH3(C2H5)NH, white, etc. Among these, those with a low boiling point and a small number of carbon atoms are desirable. Specifically, N)In, NH2NH
2, CH2NH2, C2H3NH2, (CHs)Jtl
etc.

The infusibility treatment method is not particularly limited in the present invention, and may be carried out in either a liquid phase or a gas phase.

For example, when performing the process in a liquid phase, there is a method in which the spun fibers are immersed in a solution of the above-mentioned tinnic compound for a predetermined period of time, and in this case, benzene, toluene, xylene,
Solvents such as hexane, heptane, ether, dioxane, etc., and alkali metals and alkali metal amides can be used as catalysts. The reaction temperature is usually 0 to 200'
C is preferred, and the treatment time varies depending on the reaction temperature,
It usually ranges from several tens of seconds to several hours. On the other hand, when conducting in the gas phase, the nitrogen-containing compounds are NH3, CH, NH2, C
It is desirable to use a low boiling point compound such as 2H, N82, and the reaction temperature is usually 0 to 500°C, preferably 50°C.
The range of the temperature range from 400°C to 400°C and the treatment time vary depending on the reaction temperature as described above. It is also possible to use a catalyst.

Subsequently, the infusible fibers are heated in vacuum or with nitrogen,
The silicon carbide fibers are heated in an inert gas atmosphere such as helium, neon, argon, krypton, etc. at about 800 to 2000"C for several minutes to 10 hours to obtain the desired silicon carbide fibers.

As a feature of the silicon carbide fiber manufacturing method of the present invention,
As explained in the examples below, ceramics (S
iC) High yield and very little free carbon and silica in the fired fibers.

For example, polycarbosilane consisting of the following repeating structural units is currently used as a prepolymer for SiC fibers, but although the yield of ceramics when made into fibers is moderate, it does not contain free carbon (about 10iyt%). There are many
Furthermore, when used as fibers, SiOz (approximately 20 wt%) is mixed in during the infusibility treatment using oxygen during the spinning process, and these are said to have an adverse effect on fiber strength.

Since the fibers of the present invention are made infusible using a nitrogen-containing compound instead of oxygen, almost no silica remaining in the fibers is observed, and combined with the low carbon content, the fibers have excellent fiber strength. This is also due to the fact that 5i3N4 (silicon nitride) contained in the infusible treatment does not have a negative effect on fiber strength unlike silica.

Thus, according to the present invention, fibers with unprecedented high-temperature strength can be obtained.

Reflecting the low carbon and silica content, the silicon carbide fibers of the present invention have far superior high-temperature strength compared to fibers produced by conventional methods, as shown in the Examples below.

Although it is not clear why the method of the present invention has a high ceramic yield and little free carbon in the fibers, the 5i-H bonds of the 5i83 groups are first broken and crosslinked during the thermal decomposition process, forming oligomers. It is presumed that this is because the decomposed hydrogen is less likely to scatter out of the system, and this decomposed hydrogen prevents carbonization of the polymer.

〔Example〕

Hereinafter, the present invention will be explained by examples.

Example 1 36.7 g of vinylsilane was synthesized by a hydrosilylation reaction of SiH4 and acetylene under a nitrogen atmosphere.

Titanium trichloride type catalyst for olefin polymerization (manufactured by Toho Titanium Co., Ltd.) 1 g, AI (i-CJq) + 3.3 ml,
11-Heptane 150mF! was charged into an autoclave with a capacity of 200 d, and reacted at 70°C for 4 hours. After the reaction was completed, the reaction solution was poured into methanol to remove the catalyst residue in the polymer and simultaneously precipitate the produced polymer. The obtained polymer weighed 19 g, and it was confirmed from the results of rR1 elemental analysis etc. that it was a polymer having a repeating structural unit of -f-CI+2-CH→-3iH+. This polymer is stable in air at room temperature and has a
The 5iHs group suddenly disappeared at ℃ and a siloxane bond was formed. Also, the crystallinity is about 60% and the melting point is 170 to 180.
It was ℃. The average molecular weight was approximately 100,000 (based on the viscosity method; the same applies hereinafter).

This polymer was spun using a melt spinning method, and then 40"
A contact time of about 1 is passed through a dioxane solution containing 40 wt% n-propylamine and 5 wt% potassium set at C.
(0 minutes) to obtain organosilicon polymer fibers with a diameter of 10 μm.

This fiber was placed in vacuum (I Xl0-'mmHg), 10
The sample was preheated to 00°C over 10 hours, further heated to 1200'C in an argon gas atmosphere, and fired at this temperature for 2 hours to obtain SiC fibers. The ceramic yield in this fiber production is 48%, and the fiber tensile strength is 84.
The fired product was further fired at 2000°C and examined by X-ray diffraction, but the diffraction peak due to free carbon could not be tolerated.

Examples 2 to 3 Experiments were conducted in the same manner as in Example 1, except that propylsilane and butenylsilane were used instead of vinylsilane as the polymerization monomer, and the results were as follows: →C1l□-C1l□1,000CH2-CH- JI2SIH
A polymer having a repeating structural unit of 3CtLzC)IzSiHz was obtained.

Using this polymer, silicon carbide fibers were obtained in the same manner as in Example 2.

The evaluation results are shown in Table 1.

Comparative Example 1 A polycarbosilane with a repeating structural unit of: permethylpolysilane (manufactured by Shin Nisso Kako Co., Ltd., average molecular weight: 2000) having a repeating structural unit of Polymer evaluation was performed in the same manner as in Example 1, except that each of the following was used.

The evaluation results are shown in Table 1.

〔Effect of the invention〕

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 easy to spin. In comparison, it has superior characteristics such as a high ceramic yield, no oxygen uptake during the infusibility treatment process after spinning, and less free carbon and especially silica contained in the fibers. . For this reason,
This results in fibers with significantly improved tensile strength compared to conventional fibers.

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

Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1) General formula (1) ▲Mathematical formulas, chemical formulas, tables, etc.▼(1) (However, n is 0 or a positive integer from 1 to 10, and R_1 is hydrogen, an alkyl group, or an aryl group. , R_2 represents an alkylene group or a phenylene group) into a fiber by spinning a silicon-containing polymer compound containing a repeating structural unit represented by (3) The silicon carbide fiber is further heated at 800 to 2000°C in vacuum or in an inert gas. 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 butenylsilane. 4 The nitrogen-containing compound has the general formula R_1R_2NH(R_1
, R_2 is hydrogen, an alkyl group, an aryl group, or an alkenyl group).