JPH0776159B2 - Method for manufacturing silicon carbide whiskers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a silicon carbide whisker, particularly 1 μm.
The present invention relates to a method for manufacturing a large diameter silicon carbide whisker having a diameter of m or more.

Conventional technology Silicon carbide whiskers are superior in strength, elastic modulus, oxidation resistance, heat resistance, and chemical stability compared to other composite material fibers, so that composite reinforcement of ceramics, metals, plastics, etc. Has attracted attention as a material.

In this case, the role of the silicon carbide whiskers in the composite material using metal or plastics as a matrix is to improve strength, elastic modulus, and wear resistance, whereas the composite effect of silicon carbide whiskers on ceramics is The purpose is to improve the fracture toughness value of the material, and the main purpose is to improve the reliability of the ceramic composite material against fracture. The first physical property value particularly required for such a whisker for a ceramic composite material is a whisker having a cross-sectional diameter corresponding to the strength that is not destroyed by the progress of cracks in the composite material. Therefore, the larger the whisker diameter, the higher the fracture toughness value. Therefore, a silicon carbide whisker for such a ceramic composite material is particularly desired to have a diameter of 1 μm or more.

Conventionally, the manufacturing method of the silicon carbide whiskers is roughly classified into
(A) A method of crystallizing from liquid silicon carbide under high temperature and high pressure, (B) a method of dissolving carbon in a melt of metallic silicon to crystallize silicon carbide, and (C) silicon carbide from silicon carbide powder. Known methods include sublimation at high temperature to crystallize and (D) growth of silicon carbide produced by thermal decomposition reaction of a silicon compound as crystals.

However, among these methods (A) and (B), since extremely high temperature, high pressure, or a metal melt is used, there is great difficulty in production from the viewpoint of production equipment, and the method (C) has an extremely high operating temperature. Since the temperature is high, the operation is not easy, and the equipment is complicated, it is difficult to separately collect the manufactured whiskers. Therefore, all of the methods (A) to (C) have fatal defects as an industrial manufacturing method. ing.

Therefore, as a method for producing silicon carbide up to the present, the method of (D) precipitating in a whisker shape while producing silicon carbide by various thermal decomposition reactions is the mainstream, and there are various methods for this method. Proposed.
That is, as the method (D), (1) a method of solid-phase reducing silicon dioxide with carbon or metallic silicon and carbon, (2)
Known is a method of reacting an organosilicon compound or a mixture of a silicon compound and a carbonaceous compound in a gaseous state at a high temperature, and (3) a vapor phase growth method by a reaction with a fluorine-containing silicate.

Among these, the methods (2) and (3) for producing silicon carbide whiskers in the vapor phase are methods capable of producing whiskers having a diameter of 1 μm or more by appropriately selecting the reaction conditions. . However, of these methods, the method (2) performs the reaction in the gas phase, so that the amount of silicon carbide whiskers that can be produced per unit volume of the reaction chamber is extremely low and the reaction is performed at high temperature, which is an industrial problem. In the case of large-scale production, it is necessary to maintain a high temperature in a large-capacity reaction chamber, and there are problems that corrosive reaction by-products are generated. In the method (3), the fluorine-containing silicate is melted, a reduction reaction is performed by the carbon added thereto, and the generated steam is cooled to generate silicon carbide whiskers. Since the method also uses the gas phase reaction, it has the same problems as the method of the above (2), and it is necessary to handle a large amount of molten salt, which greatly limits the material of the manufacturing equipment or Problems such as the inclusion of these molten salts as impurities in the silicon carbide whiskers occur, which is not preferable as an industrial manufacturing method for the silicon carbide whiskers.

On the other hand, the method (1) of utilizing solid-phase reduction uses silicon dioxide, which is easily available, as a starting agent, and the production of industrial-scale silicon carbide whiskers is easy. Various studies have been conducted on the silicon source material for producing the silicon carbide whiskers by the method (1), and for example, (a)
A method of using the silicon content present in rice husks of rice plants as a raw material,
(B) A method using silica sand as a raw material, (c) a method using shirasu or glass waste as a raw material, (d) a method using active silica having a high specific surface area such as silica sol or silica gel as a raw material is known. ing.

In addition, according to L. Patric et al., For the production of silicon carbide whiskers by the method of the above (1), Cr, Al, Fe, Co,
It is known that Cu, Si and Au are effective, and addition of these metals and metal compounds, and various metals centering on transition metals such as Ni and addition of these metal compounds have been proposed ( For example, JP-B-50-18479, JP-A-61-22000, and JP-A-63-159300).

However, it is extremely difficult to obtain a silicon carbide whisker having a diameter of more than 1 μm by any of the above-mentioned methods by the solid-phase reduction method (1) which is an industrially advantageous production method, and even if it is produced, the raw material layer It was only observed that it grew a little only in specific parts such as the upper part and the voids.

The present invention has been made in view of the above circumstances, and has a diameter of 1 μm or more desired to improve the fracture toughness value of a ceramic compounded with ceramics, and has a small amount of powdery silicon carbide and a high purity silicon carbide whisker. It is an object of the present invention to provide a manufacturing method capable of manufacturing a large amount of lactic acid at low cost.

Means and Actions for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventor has found that a mixture of a silicon source raw material and a carbon raw material based on the solid-phase reduction method of the above (1) is used. In the method for producing silicon carbide whiskers by reacting at 1400 to 1800 ° C., the silicon source raw material is formed into a granular form having an average particle size of 50 to 1000 μm, and iron atoms are added to the silicon atoms in the silicon source raw material at 25 to 5000ppm,
When the total of cobalt atoms and nickel atoms is contained in the above mixture so as to be 200 ppm or less, 1 μm
It has been found that a silicon carbide whisker having the above diameter and having a small amount of powdery silicon carbide and high purity can be manufactured in large quantities at low cost.

That is, as a result of examining the mechanism by which whiskers are generated and grown, the present inventor found that silicon carbide whiskers produced by the reaction between a silicon source material and a carbon material are generated at a place where the silicon source material and the carbon material are in contact with each other. Is important, and it is said that the silicon source raw material and the carbon raw material are gasified or sublimated by the reaction to cause solid phase-gas phase or gas phase-gas phase reaction. However, when the particle size of the silicon source raw material is increased, the surface area becomes smaller than that of the finely divided silicon source raw material of the same weight, so the release rate of the silicon component used in the reaction becomes slower, As a result of the gradual progress of the reaction, the diameter of the generated whiskers generally becomes large, and the average particle diameter of the silicon source material is set to 50 to 10
It was found that a silicon carbide whisker having a particle size of 1 μm or more can be efficiently obtained by forming a granular shape of 00 μm.

Further, the present inventor has known that the addition of iron, cobalt, and nickel to the reaction system of the above (1) is effective in the production of whiskers, but these elements contribute to the diameter of the whiskers formed. After studying the effect, it was found that iron is an element that promotes the increase in diameter of whiskers, while cobalt and nickel are both elements that inhibit the increase in diameter. ~ 5000pp
By adjusting the content of the reaction system so that the total amount of m, cobalt, and nickel is 200 ppm or less, the silicon source raw material is made into a granular form, and the efficiency is 1 μm.
The inventors have found that the above silicon carbide whiskers can be obtained, and have completed the present invention.

Hereinafter, the present invention will be described in more detail.

The silicon source material used in the method of the present invention is
There is no particular limitation as long as it is a solid substance that does not become a liquid phase at a temperature of 1400 to 1800 ° C, and examples thereof include silica sand, silica gel, metallic silicon, molybdenum disilicide and the like. That is, one feature of the present invention is that the silicon source material is used in a granular form having a predetermined particle size. If the silicon source material melts at the reaction temperature and undergoes a phase change from a solid phase to a liquid phase. However, the granular silicon source material having a predetermined particle size is melted and the effect of the present invention cannot be exhibited. If impurities other than silicon and carbon that constitute the silicon source material are contained, the impurities may be taken into the silicon carbide whiskers and reduce the purity. Therefore, the silicon source material may have high purity. preferable.

In particular, in terms of the yield of silicon carbide whiskers to be produced and the suppression of the content of powdery silicon carbide, the general formula R _a SiCl _4-a (wherein R is a hydrogen atom or a monovalent hydrocarbon group, and a is 0 to 3). And an chlorodisilane represented by the general formula R _b Si ₂ Cl _6-b (wherein R is a hydrogen atom or a monovalent hydrocarbon group, b is an integer of 1 to 5) A hydrolysis product obtained by hydrolyzing a single substance or a mixture is preferable. These chlorosilanes and dichlorosilanes are usually produced in the silicone industry or are by-produced, are inexpensive, and have the advantage that they can be easily purified to a high degree by distillation.

Examples of the above chlorosilanes include CH ₃ SiCl ₃ and (CH ₃ ) ₂ SiC
l ₂ , (CH ₃ ) ₃ SiCl, (CH ₂ = CH) SiCl ₃ , C ₆ H ₅ SiCl ₃ , HSiCl ₃ ,
H ₂ such as SiCl _2, SiCl ₄ are exemplified, and as the chloro _{disilanes, (CH 3) Si 2 Cl} 5, (CH 3) 2 Si 2 Cl 4, (CH 3) 3 S
i ₂ Cl _3, is exemplified and _{(C 6 H 5) 3 Si} 2 Cl 3. As the chlorosilanes or chlorodisilanes, various kinds of chlorosilanes or chlorodisilanes having a value of 0 to 3 and b value of 1 to 5 in the above general formula are obtained. These chlorosilanes and chlorodisilanes usually contain metallic impurities such as iron, cobalt and nickel components, and when used as a silicon source raw material, silicon is used in view of concentration control of iron, cobalt and nickel components. The metal impurities can be removed by a method such as a simple distillation method or a distillation / purification method before being used as a raw material for obtaining a source raw material.

The hydrolysis product of silanes used as a silicon source material is easily hydrolyzed by directly contacting the gas or liquid of the above-mentioned chlorosilanes or chlorodisilanes with water to form the ≡Si-Cl bond. Changes to ≡Si-O bond,
It becomes a hydrolysis product containing silicon and oxygen as main components. The hydrolysis product thus obtained may be
After being adjusted and dried, it is sent to the next step.

The silicon source material according to the present invention is used in the reaction in a granular form in order to reduce the reaction surface area, and it is necessary that the average grain size of the granular form is 50 to 1000 μm.
It is particularly preferable that the thickness is 100 to 500 μm. Average particle size is 50
If it is smaller than μm, the diameter of the whiskers to be formed becomes 1 μm or less, and if it exceeds 1000 μm, the reaction rate is extremely lowered, the productivity and the conversion rate of silicon to silicon carbide are lowered, and both reach the object of the present invention. I don't get it. Therefore, when the diameter of the silicon source material is 1000 μm or more, it is necessary to pulverize it, and when it is 50 μm or less, it is necessary to granulate and use it as a granular form having a particle size of 50 to 1000 μm for the reaction. In the case of granulating, a binder may be used if necessary so long as it does not inhibit whisker formation.

The carbon raw material used in the method of the present invention includes carbon blacks such as acetylene black and furnace black, carbonaceous components such as activated carbon and charcoal, and phenolic resins which are easily carbonized by heating. Either can be used. Here, as the carbon source material, a powdery carbon material is desirable because it is the solid surface that contributes to the reaction. Of these, carbon black and powdered activated carbon having a high specific surface area and high activity are preferable.

Further, the above-mentioned raw material of the mixture of the silicon source raw material and the carbon raw material can be obtained by a known method using a V-type mixer or a paddle-type mixer, but both of them are sufficiently improved from the viewpoint of yield improvement. It is preferable to mix uniformly.

The method of the present invention adjusts the content of each element such as iron, cobalt, and nickel contained in the mixed raw material composed of the above-mentioned silicon source raw material and carbon raw material, and these are used for producing a silicon carbide whisker having a large diameter. Is an element that strongly affects That is, iron is an element that promotes an increase in the diameter of silicon carbide whiskers, and the iron content is 25 pp relative to the silicon atoms in the raw material.
If it is more than m, it will start to exert its effect. However, if the iron content is more than 5000 ppm, the silicon carbide whiskers will be in a bent form, so the content of iron atoms must be 25 to 5000 ppm relative to the silicon atoms in the raw material, especially 50
~ 2000 ppm is preferred. On the other hand, on the contrary, both cobalt and nickel are elements that prevent the diameter of silicon carbide whiskers from increasing.
If the total content of each element of cobalt and nickel exceeds 200 ppm with respect to the silicon atoms in the raw material, the increase in diameter of silicon carbide whiskers is hindered, so the total content of each element of cobalt and nickel is the silicon atom in the raw material. However, it is necessary to be 200 ppm or less, and particularly preferably 100 ppm or less.

Therefore, when the content of iron does not reach 25 ppm, it is added so as to have the above content, on the contrary, when the content of iron is 5000 ppm, the total content of cobalt and nickel exceeds 200 ppm, the physical or It is necessary to chemically remove a part of these components to adjust the content to the above range.

In this case, various compounds such as iron metals, alloys, and oxides can be used as the iron component to be supplied from the outside, but in the method of the present invention, the yield of silicon carbide whiskers to be produced is improved and From the standpoint of suppressing the by-product of powdery silicon carbide, it is particularly preferable that the iron component be evenly distributed with respect to the silicon source material. Therefore, it is preferable to use the iron component in a liquid form, and when the silicon source raw material or the mixture raw material in which the carbon raw material is added to the raw material of the silicon source raw material is treated with the iron component solution, the iron component is uniformly distributed on the surface of these raw materials. It is possible to obtain silicon monoxide whiskers having a high yield and a lower content of powdery silicon carbide.

The mixture raw material of the silicon source raw material and the carbon raw material in which the contents of the iron, cobalt, and nickel components and the particle size of the silicon source raw material are adjusted in this manner are heated to form silicon carbide whiskers. In this case, this reaction can be carried out in an atmosphere of only an inert gas, but it is preferably carried out in a gas atmosphere of 1 to 100% by volume of hydrogen gas and an inert gas. The effect of this hydrogen gas is particularly remarkable when a hydrolysis product of chlorosilanes or chlorodisilanes is used as a silicon source material. Since nitrogen gas may generate silicon nitride, it is desirable not to include it in the atmospheric gas.

When the silicon source whiskers are obtained by reacting the silicon source raw material and the carbon raw material at a high temperature under the above atmosphere, the reaction temperature is 1400 to
1800 ℃, especially 1500 ~ 1700 ℃ is desirable, if it is lower than 1400 ℃, the reaction rate may be too slow, and substantial reaction may not occur. Tends to become.

In the method of the present invention, the silicon source material is the above-mentioned granular material having a predetermined particle size. In this case, the larger the particle size, the larger the whisker diameter to be formed, but the reaction The property tends to decrease as the particle size increases, and the conversion rate of the silicon source material to silicon carbide decreases, leaving unreacted silicon source material. Therefore, it is preferable to select a small particle size within the range of the particle size of the silicon source material described above, depending on the desired diameter of the silicon carbide whiskers.

Since the silicon carbide whiskers thus obtained usually contain excess carbon, they are oxidized in an air stream at 600 to 800 ° C to remove carbon and further remove unreacted silicon source. Therefore, it is preferable to treat with hydrofluoric acid or the like.

When the silicon carbide whiskers having an average diameter of 1 μm or more obtained by the above method are compounded with ceramics such as alumina and silicon nitride, it is possible to give these ceramics a high fracture toughness value.

EFFECTS OF THE INVENTION As described above, the method of the present invention is industrially advantageous, but in the solid-phase reduction method in which it was practically difficult to obtain whiskers of 1 μm or less, 1 μm or more, usually 1 to 4 μm Since it is possible to selectively obtain silicon carbide whiskers having a diameter of, and to obtain silicon carbide whiskers having a high purity with a small amount of powdery granular hydrocarbon by-products, it is desired to increase the fracture toughness value of ceramics. It is possible to manufacture silicon carbide whiskers in large quantities at low cost.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

In the following examples, analysis of iron, cobalt and nickel was performed by IPC emission spectroscopy, and the ratio of whiskers and powdery particles in the produced silicon carbide was visually inspected to obtain one of the five levels shown in Table 1. The content of powder and granules was evaluated by the evaluation value.

Example 1 Iron purified by distillation, nickel, methylchlorodisilanes mixture content was respectively set to 5ppm or less of cobalt (trimethylchlorosilane disilane _{[(CH 3) 3 Si 2 Cl} 3 ] dimethyl tetrachlorodisilane [(CH ₃ ) ₂ Si ₂ Cl ₄ ]: 1: 1 mixture) 108.9g is poured into pure water in which 0.054g FeCl ₃ .6H ₂ O is dissolved and hydrolyzed to form a white gel-like hydrolysis product. After the product was prepared, it was dried to completely remove the water content, and a granular hydrolysis product (silicon source material) was obtained. The concentration of iron relative to silicon atoms in this hydrolysis product was 391 ppm, cobalt,
Nickel was below 5 ppm each.

Next, the granular hydrolysis product is crushed, pressure-molded,
The operation of sieving was repeated, and the total amount of the hydrolysis product was granulated to 100 to 150 μm to obtain 60.7 g of a granular silicon source raw material. 36 g of carbon black as a carbon source material was mixed with this silicon source material, sufficiently stirred and then loaded into a furnace,
While flowing a mixed gas of argon gas and hydrogen (Ar: H ₂ = 7: 3) in the furnace, the temperature of the furnace was raised to 1600 ° C, and the reaction was performed at 1600 ° C for 2 hours to manufacture silicon carbide whiskers. After furnace cooling, the resulting reaction product is oxidized in the air at 750 ° C for 1 hour and then immersed in 50% hydrofluoric acid for 1 hour to remove unreacted carbon black and unreacted silicon source. did.

The weight of the reaction product (silicon carbide) after the above treatment was 23.6 g, and the conversion rate of silicon atoms in the hydrolysis product to silicon carbide was calculated from the content ratio of silicon atoms in the hydrolysis product. Was 59%. The diameter of the generated silicon carbide whiskers is 1.
The evaluation value of the content of powdery particles was 2 μm, and therefore a large-diameter silicon carbide whisker containing almost no particles could be obtained.

[Comparative Example 1] The same amount of the same methylchlorodisilane mixture as in Example 1 was used as Fe.
Cl ₃ · 6H ₂ O is _{0.054g, CoCl 2 · 6H 2 O} , is hydrolyzed to put into pure to NiCl ₂ · 6H ₂ O is 0.0057g respectively dissolved to make a gel-like hydrolysis product After that, the product was dried to completely remove water, and a granular hydrolysis product (silicon source material) was obtained. The concentrations of iron, cobalt, and nickel with respect to silicon atoms in this hydrolysis product are 405 ppm, 48 ppm, and 53 ppm, respectively.
And the total concentration of cobalt and nickel was 101 ppm.

This hydrolyzed product was crushed, pressure-molded and sieved in the same manner as in Example 1 to form a total amount of 100 to 150 μm in a granular form, which was then mixed with carbon black and reacted by heating. Of carbon black and silicon source were removed.

The conversion rate of the obtained reaction product (silicon carbide) was 75%, and the evaluation value of the content of powdery particles was 1, but the silicon carbide whiskers had an average diameter of 0.6 μm, 1
It was about half of that obtained in.

[Examples 2 to 9 and Comparative Examples 2 to 6] The same methylchlorodisilane mixture as in Example 1 was used, hydrolyzed with pure water in which predetermined iron, cobalt, and nickel were dissolved, and then dried. Hydrolysis products having the contents of iron, cobalt and nickel shown in Table 2 were obtained.

Next, the hydrolysis product adjusted to a predetermined particle size as in Example 1 was mixed with carbon black and reacted at the temperature shown in Table 2 in the same manner as in Example 1, and then with unreacted carbon black. The silicon source was removed to obtain silicon carbide (silicon carbide whiskers).

Table 2 shows the conversion rate of the obtained silicon carbide, the average diameter of the silicon carbide whiskers, and the evaluation value of the content of the particulate material. The results of Example 1 and Comparative Example 1 are also shown in Table 2.

Front page continued (72) Inventor Kazutoshi Numanami 1 in 28, Nishi-Fukushima, Chugiki-mura, Nakakubiki-gun, Niigata Prefectural Shin-Etsu Chemical Co., Ltd. Synthetic Technology Laboratory (72) Inventor Takahiro Iizuka, Nishikaku, Naka-kubiki-gun, Niigata Nishi 28 Fukushima No. 1 Synthetic Technology Laboratory, Shin-Etsu Chemical Co., Ltd.

Claims (1)

[Claims] 1. A mixture of a silicon source raw material and a carbon raw material is 1400 to
In the method for producing silicon carbide whiskers by reacting at 1800 ° C., the silicon source raw material is formed into a granular form having an average particle size of 50 to 1000 μm, and iron atom is 25 to 5000 ppm, cobalt based on silicon atom in the silicon source raw material. A method for producing a silicon carbide whisker, characterized in that the total amount of atoms and nickel atoms is contained in the above mixture so as to be 200 ppm or less.