JPH06166510A - Method for producing fine particle silicon carbide - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for always producing high-quality fine particle-shaped silicon carbide with good operability, without leaving unreacted raw material components and by-produced silicon carbide in a different shape. In a method of heating a mixed raw material composed of a silica source and a carbonaceous material to a temperature of 1300 to 2000 ° C. in an inert atmosphere to convert it into silicon carbide powder by a reducing carbonization reaction of the silica source, colloidal silica is added to the silica source. Carbon black having a carbon content of 99% or more and a sulfur content of 0.2% or less, a BET specific surface area of 80 m ² / g or less, and a DBP oil absorption amount of 60 ml / 100 g or more is used as the carbonaceous material. The composition of the mixed raw material is set within the range of 1.6 to 2.2 in terms of C / SiO ₂ molar ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing high-quality particulate silicon carbide without the generation of unreacted components and by-products such as whiskers.

[0002]

2. Description of the Related Art Conventionally, as a method for producing silicon carbide powder, a reducing carbonization method in which silica is heat-treated with a carbonaceous material, a gas phase reaction method in which a silicon halide compound and hydrocarbon are heated and reacted in a gas phase system, and an organic silicon are used. A thermal decomposition method in which a compound undergoes a thermal decomposition reaction is known. Among them, the gas phase reaction method and the thermal decomposition method can generate fine-grained silicon carbide of submicron grade or less, but the silicon halide compound or the organic silicon compound used as a raw material is expensive. In addition to being a difficult substance to handle, the production yield is low, so there are many problems as an industrial production means.

In this respect, the reduction carbonization method has long been regarded as a basic technique for industrially producing silicon carbide powder because it can be mass-produced by a relatively simple furnace operation called the Acheson method. However, since this method employs a process in which an ingot of silicon carbide is once generated and then crushing and classifying steps are repeated to adjust to a desired particle size, there is a limit to the powder particle size to be obtained, and the crushing is also difficult. There is a drawback that a high-purity product cannot be manufactured due to the inclusion of impurities in the process.

Thereafter, in each industrial field, there has been an increasing demand for development of submicron-class fine particles of high-purity silicon carbide, and in order to meet this demand, silicon carbide which changes the raw material system into various compositions or forms while using the reducing carbonization method as a basic technology. A method for producing powder has been proposed. For example, a method of uniformly dispersing or dissolving carbon or a carbon compound in a silica source solution, gelling and drying, and then synthesizing silicon carbide (Japanese Patent Laid-Open Publication No. S60-187242).
58-104010), a decomposable silicon compound such as silicon tetrachloride and trichlorosilane and a hydrocarbon compound such as methanol, benzene, kerosene, and creosote oil are fed into a hot gas containing water vapor to oxidize silicon. A method of producing and collecting a mixed aerosol containing a substance and elemental carbon and igniting the aerosol to produce a silicon carbide powder having a high specific surface area (Japanese Patent Laid-Open No. 58-213621) and the like correspond to this. However, in the case of the former method, a step of adding a surfactant when mixing a silica source solution and carbon or a carbon compound or a step of gelling by adjusting pH after preparing a uniform mixed raw material is required. However, in the latter method, it is possible to prepare a homogeneous mixed raw material to some extent continuously, but the decomposable silicon compound contains a difficult-to-handle halide, which complicates the equipment. There is an unavoidable problem of complication and operational complexity.

As a method for producing ultrafine silicon carbide powder, a method in which silica powder and carbon black having a specific surface area of 1 to 1000 m ² / g are granulated with various binder components and then continuously heated and reduced (JP-A-59-39709 and JP-A-59-190208) have also been proposed. In this method, carbon black whose particle properties are relatively easy to control is used as the carbonaceous material, so that there is an advantage that the conditions for obtaining fine silicon carbide powder can be easily adjusted. It is also possible to accelerate the reducing carbonization reaction by selectively using fine particle carbon black having a large specific surface area.
However, when carbon black having a too large specific surface area is used, on the contrary, the conversion efficiency of silica to silicon carbide is decreased, and at the same time, the partial pressure of SiO gas is increased to promote crystallization of particles and a large amount of whiskers are by-produced. Will be invited.

[0006] The applicant has begun to use BE as a carbonaceous material in the reduction carbonization method in order to avoid such a phenomenon and to produce fine-grained silicon carbide of good quality with no by-products of whiskers.
T specific surface area 80m ² / g or less, DBP oil absorption 100ml / 100g
The composition of the mixed raw material is C, using carbon black having the following characteristics and the aggregate Stokes mode diameter of 1 μm or less.
A method for setting the condition of / SiO _{2 to} be 3.5 or more has been developed and already proposed as Japanese Patent Application No. 3-321074.

[0007]

DISCLOSURE OF THE INVENTION The present inventor has found that the relationship between the characteristics of carbon black used when producing silicon carbide powder by a reduction carbonization method using carbon black as a carbonaceous material and the properties of the silicon carbide powder produced. In the process of continuing multifaceted research, the colloidal silica was selected as the silicon source, the purity characteristics and particle characteristics of the carbonaceous carbon black were specified, and the raw material mixture composition was set within a certain range. It was confirmed that the fine particle silicon carbide can be obtained without any residual component or by-product.

The present invention was developed on the basis of the above-mentioned findings, and its purpose is to prevent residual unreacted raw material components and by-products of silicon carbide in different forms such as fibrous, whisker-like and coarse particles. The object of the present invention is to provide a method for always producing high-quality fine particle silicon carbide with good operability.

[0009]

In order to achieve the above-mentioned object, a method for producing fine particulate silicon carbide according to the present invention comprises a mixed raw material comprising a silica source and a carbonaceous material in an inert atmosphere.
In the method of heating to a temperature of 0 to 2000 ° C. to convert to a silicon carbide powder by a reduction carbonization reaction of a silica source, colloidal silica is used as a silica source, a carbon content of 99% or more as a carbon material, and a sulfur content of 0.2. % Or less purity characteristics, B
ET specific surface area 80m ² / g or less, DBP oil absorption 60ml / 100g
The carbon black having the above particle properties is used, and the composition of the mixed raw material is C / SiO ₂ molar ratio of 1.6 to 2.2.
The characteristic feature of the configuration is to set the value within the range.

In the present invention, colloidal silica is selectively used as the silica source. There are no particular restrictions on the dispersion concentration of the sol, the alkali ion component, etc., but normally, a dispersed silica particle having a particle size of 1 to 100 nm and a Na ⁺ type is preferably used. The reason why colloidal silica is used as a silica source is that the mixing property with carbonaceous carbon black can be improved and the carbonaceous material can be uniformly impregnated and dispersed even inside the carbonaceous structure. When powdery silica raw materials are used, it is inevitable that poor dispersion will occur during mixing. In addition, since silica components do not enter the carbonaceous structure even when wet-stirring ultrafine silica such as Aerosil with carbon black in the presence of an organic solvent,
The reducing carbonization reaction at the raw material interface does not proceed smoothly.

The type and production history of carbon black used for the carbonaceous material are not particularly limited, and various types such as furnace black, acetylene black and thermal black can be applied. It must meet the specified property requirements. Of these, a carbon content of 99% or more and a sulfur content of 0.2
The purity characteristic of not more than% is a condition necessary for suppressing the formation of fibrous substances containing whiskers during the reduction carbonization reaction, and when the carbon content is less than 99% and the sulfur content exceeds 0.2%. Gasification of the reaction components is promoted, and vapor phase products such as fibrous silicon carbide are easily generated. Also, if the impurities contained are F
In the case of a transition metal such as e, Co or Ni, these components act as a catalyst to accelerate the formation of whiskers.

In addition to the above-mentioned purity characteristics, the carbonaceous carbon black must have particle characteristics such that the BET specific surface area is 80 m ² / g or less and the DBP oil absorption is 60 ml / 100 g or more. BE
If the T specific surface area exceeds 80 m ² / g, the reaction will proceed too much and the by-products of the fibrous material will increase. Also, the DBP oil absorption is 60 ml / 100
If it is less than g, the agglomeration structure is insufficient and slurry is formed when impregnating the colloidal silica. Therefore, the dried colloidal silica is solidified and segregated into a glassy state, and unreacted SiO ₂ is likely to remain. In addition, regarding each characteristic value that is an evaluation index of particle properties, regarding BET specific surface area (N ₂ SA), ASTM D3037-78 “Standard Method of Testing
Carbon Black-Surface Area by Nitro-gen Adsorptio
n "Method C, on the other hand, DBP oil absorption is JIS K6
221 (1975) "Testing method for carbon black for rubber" 6.1.2
The value obtained by the oil absorption amount A method in the section shall be applied.

The mixed raw material composed of colloidal silica and carbon black carbonaceous material is preferably prepared so that both components are uniformly dispersed and a silica source enters the inside of the carbonaceous material structure. An effective mixing means for this purpose is a method in which both raw material components are sufficiently kneaded using a powerful stirring device, or a method in which carbonaceous carbon black is tumbled and granulated using a silica sol solution as a granulating liquid. In the case of granulating, a pin-type granulator applicable to pelletizing carbon black can be used as an apparatus.

The composition of the mixed raw material is set so that the molar ratio of C / SiO ₂ is within the range of 1.6 to 2.2.
When the molar ratio is less than 1.6, the conversion rate of silica to silicon carbide decreases, and the amount of unreacted silica remaining increases, and
If it exceeds 2, the carbon source becomes excessive and the amount of unreacted free carbon increases.

The prepared mixed raw material of silica and carbon black is filled and sealed in a reaction vessel made of a highly heat-resistant material such as graphite, and placed at 1300 to 2000 ° C. in a heating furnace kept in an inert atmosphere. Heat reaction in the temperature range of. The silicon carbide recovered after the reaction is of high quality, having a free carbon content of less than 2%, a residual SiO ₂ content of less than 1% and a particle size of 1 μm or less, which is unreacted as required by the prior art. The residual carbon black component can be commercialized as it is without performing post-treatment such as combustion removal in the air or chemical cleaning of the residual silica component to remove it.

[0016]

The mechanism of producing the silicon carbide powder according to the present invention proceeds through a two-step reductive carbonization reaction according to the following equations (1) and (2). SiO ₂ (s) + C (s) → SiO (g) + CO (g) (1) SiO (g) + 2C (s) → SiC (s) + CO (g) (2) Therefore, the generation of silicon carbide Although it depends on the gas-solid reaction of the equation (2), when the reaction rapidly progresses, the generated particles become coarse or move to the gas phase reaction to increase the by-products of fibrous silicon carbide such as whiskers. In addition, the production yield of particulate silicon carbide is reduced.

According to the raw material combination of the colloidal silica and the carbon black carbonaceous material having the specific property according to the present invention, the reaction of the above formula (2) proceeds smoothly and suppresses the transition to the gas phase reaction, and the coarse particles and fibers are Fine particles of silicon carbide are predominantly produced without accompanying by-products. In addition, the raw material composition is C /
By setting the SiO ₂ molar ratio to be 1.6 to 2.2, unreacted silica and carbonaceous material components do not remain, so that it is not necessary to perform a complicated post-treatment for removing these components. . Such actions synergistically make it possible to always manufacture high-quality fine particle-shaped silicon carbide having a uniform particle size of 1 μm or less with good operability.

[0018]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 4 and Comparative Examples 1 to 6 Various silica sources shown in Table 1 and carbon black carbonaceous materials were thoroughly mixed with a universal stirrer (manufactured by Dalton Co., Ltd.), dried and then made of graphite. Fill the reactor with a graphite lid on top and place in a high-frequency furnace maintained in a nitrogen gas atmosphere at 20 ° C.
The temperature rises to 1600 ° C at a heating rate of / min and
It was held for a time to cause a reduction carbonization reaction. Table 2 shows the properties of the silicon carbide powder recovered after the reaction.

[0020]

[Table 1]

[0021]

[Table 2]

As is clear from comparison between Tables 1 and 2, the silicon carbides according to the examples are homogeneous fine particles having a particle size of 1 μm or less with a small amount of unreacted components, and their specific surface area range is 10 μm.
It was in the range of up to 30 m ² / g, and it was a property as it was as a product. On the other hand, the silicon carbide of the comparative example, which is out of the requirements of the present invention, does not become normal fine particles or requires a post-treatment to remove a large amount of unreacted components.

[0023]

As described above, according to the present invention, colloidal silica is used as a silica source, carbon black having specified purity characteristics and particle characteristics is used as carbonaceous material, and the raw material composition is set within a predetermined range for reduction. By applying the carbonization process, it is possible to manufacture high-quality submicron-grade fine-grained silicon carbide with good operability without the need for complicated post-treatment. Therefore, it is extremely useful as a manufacturing technique for the purpose of producing silicon carbide powder for sintering.

Claims (2)

[Claims] 1. A method of heating a mixed raw material comprising a silica source and a carbonaceous material to a temperature of 1300 to 2000 ° C. in an inert atmosphere to convert it into a silicon carbide powder by a reducing carbonization reaction of the silica source, wherein the silica source is colloidal. Using silica as a carbonaceous material, a carbon content of 99% or more, a sulfur content of 0.2% or less, and a BET specific surface area of 80 m ² / g or less, DBP
Particulate silicon carbide characterized by using carbon black having a particle property with an oil absorption amount of 60 ml / 100 g or more and setting the composition of the mixed raw material within the range of 1.6 to 2.2 in terms of C / SiO ₂ molar ratio. Manufacturing method. 2. Free carbon amount less than 2%, residual SiO ₂ amount 1
The method for producing fine particle silicon carbide according to claim 1, wherein silicon carbide having a particle diameter of 1 μm or less is produced in an amount of less than 1%, and the product is commercialized without post-treatment for removing unreacted components.