JPH03359B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial field of application] The present invention is a method for producing large aspect ratio
This invention relates to a method for producing SiC whiskers. [Prior Art] SiC whiskers are attracting attention as reinforcing materials for composite materials because they have extremely excellent strength and elastic modulus, as well as high heat resistance and corrosion resistance, and are lightweight. In particular, in recent years it has become useful as a reinforcing material for FRM, FRP, and FRC in a wide range of application fields including automobiles and aircraft. Generally, SiC whiskers with excellent reinforcing properties are required to have long fiber length and a large aspect ratio. There are two methods for producing SiC whiskers: a gas phase method in which a silicon-containing raw material and a carbon-containing raw material are reacted in the gas phase, and a solid-phase method in which solids are used as both the silicon-containing raw material and the carbon-containing raw material. be. Gas phase methods include, for example, a method in which a silicon compound such as SiCl ₄ or (CH ₃ ) ₄ Si is reacted with a carbon compound such as CH ₄ , C ₃ H ₈ , or CCl ₄ in a high-temperature hydrogen stream, or a method in which a silicon compound such as SiCl 4 or (CH _{3 ) 4} Si is reacted in a high-temperature hydrogen stream; There is a method of thermally decomposing a silane compound such as SiCl ₃ in a hydrogen stream. However, if SiC whiskers with longer fiber lengths and higher aspect ratios can be obtained, they can be easily made into sheets or continuous into long fibers, making it possible to apply them in a wider range of fields. It is generally known that the presence of hydrogen sulfide during the SiC whisker generation process accelerates the whisker growth reaction. Hydrogen sulfide reacts with silicon-containing decomposition products to produce silicon sulfide, which in turn reacts with carbon-containing decomposition products.
It is thought that it converts into SiC whiskers. To utilize the whisker generation promoting function of hydrogen sulfide, mercapto-modified silicone oil can be used with hydrogen or argon as a carrier gas.
SiC by pyrolysis at a temperature of 1200-1400℃
A method of generating whiskers has been proposed.
(January 1988 Ceramics Basics Discussion Meeting Materials). SiC whiskers produced by this method have a diameter of 0.3 to 3 μm and a length of several
Long whiskers reaching cm have been obtained. However, the mercapto-modified silicone oil used as a raw material is expensive, difficult to obtain, and has shortcomings such as poor long-term stability. [Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks and provides a method for efficiently producing long whiskers with a large aspect ratio using readily available and inexpensive raw material systems. This is what we provide. [Means for Solving the Problems] That is, the method for producing SiC whiskers of the present invention involves adding a sulfur-containing substance to a carbon-containing silane compound and dissolving or dispersing the raw material in a hydrogen atmosphere at 1200 to 1600 °C. The structural feature is heating to a temperature of °C. The silane compounds used in the present invention include those having carbon-containing groups such as alkyl groups and alkoxyl groups in their constituent molecules, such as (CH ₃ ) ₄ Si,
(CH ₃ ) ₂ SiCl ₂ , Si(OC ₂ H ₅ ) ₄ , etc. are used. These silane compounds thermally decompose when heated in a hydrogen atmosphere to produce decomposition products containing silicon and decomposition products containing carbon. Note that in order to adjust the amount of decomposition products containing carbon, hydrocarbons such as CH ₄ and C ₃ H ₈ can also be separately supplied in addition to the silane compound. In this case, when a sulfur-containing substance is added to the silane compound, the sulfur-containing substance is also thermally decomposed to produce hydrogen sulfide. The generated hydrogen sulfide reacts with silicon-containing decomposition products to convert into silicon sulfide, and silicon sulfide then reacts with carbon-containing decomposition products.
Converts to SiC and grows into long whiskers. As the sulfur-containing substance, sulfur-containing hydrocarbons such as thiophene, dimethyl sulfide, and dimethyl sulfoxide, or elemental sulfur and hydrogen sulfide are preferably used. This sulfur-containing substance is supplied to the reactor in a state in which it is dissolved or dispersed in a silane compound. The appropriate amount of the sulfur-containing substance added is 0.05 to 10 wt% relative to the silane compound in terms of sulfur content. This is because if the amount added is less than 0.05 wt%, the amount of silicon sulfide produced is small and the whisker production reaction does not proceed efficiently. Moreover, if it exceeds 10 wt%, excess silicon sulfide will remain unreacted and will be discharged from the reaction system, which is not preferable. When this silane compound raw material containing a sulfur-containing substance is introduced into a reactor using hydrogen as a carrier gas and thermally decomposed at a temperature of 1200 to 1600°C in a hydrogen atmosphere, SiC whiskers are formed on a substrate placed in the reactor. generate. Graphite, alumina, or the like is used as the substrate. The raw material is introduced into the reactor as a liquid at a ratio of 0.005 to 0.04 Vol.% relative to hydrogen gas. If it is less than 0.005 Vol.%, the generation efficiency of SiC whiskers is poor, and if it exceeds 0.04 Vol.%, the generated pyrolytic carbon will be mixed in the SiC whiskers.
This is because there may be cases where its removal becomes necessary.
The hydrogen gas introduced is set at a speed of about 10 to 180 cm/min over the substrate. This is because if the speed is less than 10 cm/min, the SiC whisker generation efficiency is poor, and if the speed is more than 180 cm/min, the generation efficiency is reduced. Under these conditions, by holding at the specified temperature for 0.5 to 4 hours, it is possible to form a specimen with a diameter of 0.1 to 2μ and a length of several centimeters.
SiC whiskers can be efficiently produced. [Operation] Based on the above configuration, silicon sulfide having the function of promoting the growth of SiC whiskers can be effectively produced using an inexpensive and easily available raw material system. [Example] Example 1 A mullite reactor tube (inner diameter 80 mm,
(length 1600 mm) was inserted and both ends were sealed with graphite plugs. A SUS316 raw material introduction pipe (inner diameter 1 mm) and a hydrogen gas supply pipe (inner diameter 6 mm) were inserted into one end, and an exhaust pipe (inner diameter 15 mm) was inserted into the other end. In addition, a mullite substrate was installed in the center of the reactor tube. First, the temperature was raised while flowing argon gas to replace the air in the reactor tube, and then hydrogen gas was switched to create a high-temperature hydrogen atmosphere in the system. In this way
Raw materials prepared by dissolving 15 g and 25 g of thiophene in 100 g of dimethyldichlorosilane were introduced into a reactor tube set at 1300° C. at a rate of 0.1 ml/min. Note that the flow rate of hydrogen gas was set at 500 ml/min.
Table 1 shows the shape characteristics and yield of SiC whiskers obtained by holding under these conditions for 2 hours. For comparison, mercapto-modified silicone oil (X-22-980 manufactured by Shin-Etsu Chemical Co., Ltd.) was used as a raw material.
The shape characteristics and yield of SiC whiskers produced using the same method as in Example 1 under other conditions are also listed in the same table.

[Table] Example 2 Silicone oil (KF-96 manufactured by Shin-Etsu Chemical Co., Ltd.) 100g
The same method as in Example 1 was carried out except that raw materials in which 4 g and 15 g of thiophene were dissolved were used. The results obtained are shown in Table-2. Although thermal decomposition was performed under the same conditions using only silicone oil and a raw material without thiophene added, no generation of SiC whiskers was observed.

〔Effect of the invention〕

As is clear from the above explanation, the method of the present invention is inexpensive, easily available, and uses stable raw material systems to produce fibers with long fiber length and large aspect ratio.
It becomes possible to efficiently manufacture SiC whiskers.

Claims (1)

[Claims] 1. A method for producing SiC whiskers, which comprises heating a raw material prepared by adding a sulfur-containing substance to a carbon-containing silane compound and dissolving or dispersing the mixture to a temperature of 1200 to 1600°C in a hydrogen atmosphere. . 2. The method for producing SiC whiskers according to claim 1, wherein the sulfur-containing substance is a sulfur-containing hydrocarbon, elemental sulfur, or hydrogen sulfide. 3 Adding a sulfur-containing substance to a silane compound as sulfur
The method for producing SiC whiskers according to claim 1, wherein 0.05 to 10 wt% is added.