JPH03358B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing SiC whiskers useful as composite reinforcing materials for metals, ceramics, plastics, and the like. [Prior art] Various factors are involved in the SiC whisker production reaction, including the types of Si source raw materials and carbon materials used, the blending ratio of these raw materials, the mixing method, the reaction atmosphere and temperature, and the type of catalyst. However, the quality and yield of whiskers obtained are largely controlled by these conditional factors. In particular, SiO ₂ powder as a Si source raw material,
In the production reaction of a solid-phase raw material system that uses carbon powder as the carbonaceous material, it is possible to produce high-quality SiC whiskers that do not contain shot by adopting a mixing method that creates a microscopic homogeneous dispersion of the raw material components and a bulgy mixed state. This is an important deciding factor for stable acquisition. Until now, a method of secondary mechanical stirring of fine powder has been widely used for mixing raw material components. When using this method, if carbon black, which inherently has an ultra-fine particle morphology, is used as a carbon material component,
The mutual dispersion with SiO ₂ powder is also considerably homogenized. Furthermore, when carbon black with a characteristic range of a large specific surface area and highly developed structure is used, the bulk of the mixture increases, so crystal formation and growth of SiC whiskers proceed effectively (Japanese Patent Application Laid-Open No. 61-127700). However, the above-mentioned mechanical stirring mixing method has the disadvantage that even if the SiO ₂ powder is made as fine as possible, it is difficult to obtain sufficient homogeneous dispersion with carbon black, and even if a homogeneous dispersion state is obtained, segregation phenomena are likely to occur during the subsequent handling process. There is. In order to overcome these difficulties, silicon oxidation is carried out by introducing decomposable silicon compounds such as SiCl ₄ and HSiCl ₃ and carbon compounds such as methanol, benzene, kerosene, and creosote oil into hot gas containing water vapor. Generates a mixed aerosol containing substances and elemental carbon,
By collecting this dispersoid, the bulk specific gravity can be reduced to 0.2
A method for producing SiC whiskers has been proposed (Japanese Patent Application Laid-Open No. 121198/1983) which produces a mixed raw material system with high uniformity of less than g/cc and fine constituent particle size. [Problems to be Solved by the Invention] The method according to JP-A-59-121198 described above has good homogeneous dispersibility because it forms a mixed aerosol of silicon oxide and elemental carbon by vapor phase thermal decomposition. However, since the Si source material uses decomposable silicon compounds such as halogens or silanes, which are difficult to handle, complexity in terms of equipment and operation cannot be avoided. [Means for solving the problem] Unlike the prior art, the present invention stably and stably produces high-quality SiC whiskers by incorporating a furnace carbon black generation method into the mixture of Si source material and carbon material. This led to the development of a manufacturing method that allows for safe mass production. That is, the configuration of the present invention is such that in the furnace carbon black generation process, in which hydrocarbon feedstock oil is injected into a high-temperature combustion gas stream to generate carbon black through a thermal decomposition reaction, the reaction is stopped by water cooling. In the subsequent high temperature system
It is characterized by introducing SiO ₂ fine powder and heating the collected C-SiO ₂ dispersion mixture to a temperature of 1300 to 1800° C. in a non-oxidizing atmosphere. The furnace carbon black generation process applied to the present invention involves rapidly converting feedstock hydrocarbon vapor into a hot combustion gas stream obtained by burning a hydrocarbon fuel and a suitable oxidizing agent including air or oxygen. The conventional oil furnace method of pyrolysis and rapid water cooling of the pyrolysis product to separate and recover the suspended carbon black can be used; It is desirable to set conditions. In the above generation process, fine powder of SiO ₂ is introduced into a stable high temperature zone after the water cooling position.
Specifying the introduction position is an essential requirement of the present invention.If SiO ₂ fine powder is introduced into the carbon black generation reaction zone before the water cooling position, a complex reaction will occur, resulting in an irregular shape that contaminates the granular SiC. Converts to carbon black. As the SiO ₂ fine powder to be introduced, finely pulverized silica, silica gel, etc., or white carbon may be used, but it is preferable to use a fine powder with a particle size of 100 μm or less. These fine powders of SiO ₂ can be injected in a solid state from an appropriate point after the water cooling position, but if you take the method of supplying it in the form of a suspension suspended in cooling water from the cooling position into the furnace. In the process of volatilization and evaporation of water, dissociation and dispersion of agglomerates occurs, further promoting homogenization, and is also practical from an operational point of view. In this case, a catalyst component that promotes the growth of SiC whiskers can be added together with or separately from the SiO ₂ fine powder into the high temperature system after the water cooling position. The effective catalyst component is a transition metal material selected from Fe, Ni or Co, which is added in the form of an aqueous solution containing dissolved inorganic salts. The C-SiO ₂ dispersion mixture produced by introducing the SiO ₂ fine powder is separated and collected from the gas stream using a collection device such as a bag filter. The raw material system consisting of the C-SiO ₂ dispersion mixture obtained in this way was filled into a graphite reaction vessel and placed in an electric furnace maintained in a non-oxidizing atmosphere for 1300~
SiC whiskers are produced by a heating reaction at 1800°C, preferably in a temperature range of 1500 to 1700°C. [Operation] According to the above structure, carbon black adheres and solidifies to the SiO ₂ particle surface through rapid mutual contact between the introduced SiO ₂ fine powder and the generated carbon black-containing gas flow, resulting in extremely uniform homogeneous dispersion and bulkiness. form a mixed state. Therefore, always high quality SiC
It becomes possible to secure a raw material system that allows stable mass production of whiskers. Furthermore, since no halogen compounds are used as raw materials, no operational troubles such as the generation of harmful gases occur during the mixing process. [Example, Comparative Example] A combustion chamber (diameter 250 mm, length 600 mm) equipped with a tangential air supply port in the furnace head, a combustion burner inserted in the axial direction of the furnace, and a raw oil injection nozzle, coaxial with the combustion chamber. A narrow-diameter reaction chamber (diameter 50 mm, length
400mm) and a wide-diameter reaction chamber (diameter 200mm, length 2000mm), with a cooling water injection nozzle for stopping the reaction in three stages at the rear of the wide-diameter reaction chamber (cooling position: wide-diameter reaction chamber). 500mm, 1000mm from the entrance,
An oil furnace equipped with 1500mm (1500mm at each position) was installed. A bag filter device for collecting powder was installed downstream of the oil furnace via an air cooling conduit. Applying this equipment, the specific gravity (15/4℃) of raw oil
1.07, viscosity (Engler, 40/20℃) 1.80, toluene insoluble content 0.03, correlation coefficient (BMCI) 145, and fuel oil with specific gravity (15/14℃) 0.980, Two types of carbon black were generated under different generation conditions using a hydrocarbon oil with a viscosity (cp/19°C) of 1.0 and a residual carbon content of 0.6. At this time, the cooling water supplied from the first stage cooling water injection nozzle has a maximum particle size of 7 μm and an average particle size of 42 μm.
SiO ₂ fine powder was suspended and a small amount of CoCl ₂ was dissolved and introduced into the furnace. The composition of the dispersion mixture of the C--SiO ₂ --Co compound finally collected by the bag filter, the properties of the contained carbon black, and other properties are shown in the table in comparison with the generation conditions. In addition, in the items in the table, the amount of introduced SiO ₂ fine powder is the weight ratio (%) to the produced carbon black,
The amount of CoCl ₂ added was expressed as a weight ratio (%) to the introduced SiO ₂ fine powder, and the C-SiO ₂ -Co compound production ratio (wt%) was determined by a combustion method and an atomic absorption spectrometry method.

[Table] Obtained dispersion mixture of C-SiO ₂ -Co compound system
After lightly filling 40 g into a high-purity graphite reaction vessel with an inner diameter of 60 mm and a height of 150 mm, a graphite lid was attached and the reactor was placed in an electric furnace, while maintaining the inside of the furnace in a non-oxidizing atmosphere.
The temperature was maintained at 1600°C for 2 hours to react and generate SiC whiskers. The reaction product was taken out from the reaction vessel and heat treated in the atmosphere at a temperature of 700°C to burn off unreacted carbon black. The physical properties of the SiC whiskers produced in this way are shown in the table. For comparison, according to the conventional mechanical mixing method, the same characteristics as Example Run No. 1 (N ₂ SA150
50 wt% SiO ₂ fine powder and 2.0 wt% CoCl _{2 based on the amount of SiO 2} ^fine powder were added to carbon black with a DBP oil absorption of 130 ml/100 g), and C-SiO ₂ was mixed with stirring using a V- _type mixer. _−CoCl2 ratio (wt%) 66.2:
The properties of SiC whiskers produced under the same conditions as in the examples using a mixed raw material having a composition of 33.1:0.7 are also listed in the table.

〔Effect of the invention〕

The present invention significantly improves the degree of homogeneous dispersion of raw material components, which largely controls the quality of produced SiC whiskers, without any operational difficulties, and thus enables stable mass production of high-quality SiC whiskers with low shot content. The industrial value is enormous because it made this possible.

Claims (1)

[Scope of Claims] 1. In the furnace carbon black generation process in which hydrocarbon feedstock oil is injected into a high-temperature combustion gas stream, carbon black is generated through a thermal decomposition reaction, and the reaction is stopped by water cooling, the furnace carbon black is generated after the water cooling position. SiO ₂ fine powder was introduced into the high-temperature system, and the collected C-SiO ₂ dispersion mixture was heated to
SiC characterized by heating to a temperature of ~1800℃
Whisker manufacturing method. 2 SiO ₂ fine powder is contained in the high temperature system after the water cooling position.
Alternatively, the method for producing SiC whiskers according to claim 1, wherein a catalyst component selected from Fe, Ni, or Co is added in an aqueous solution state. 3. The method for producing SiC whiskers according to claim 1, wherein the SiO ₂ fine powder is suspended in cooling water and introduced from the water cooling position.