JPH0454610B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing composite fine powder made of silicon nitride and silicon carbide. More specifically, the general formula is [R ¹ , R ² , R ³ , Si] ₂ NR ⁴ or [−
R ¹ , R ² , Si-NR ³ ]-n (wherein R ¹ to ^{R 4} each represent hydrogen, an alkyl group, an allyl group, a phenyl group, a methylamino group, etc., and n is 3 or 4)
This invention relates to a method for producing a fine composite powder of silicon nitride and silicon carbide, which is characterized by reacting a silazane compound represented by the following in a gas phase. Non-oxide ceramics such as silicon nitride and silicon carbide have superior high-temperature properties such as high-temperature strength and thermal shock resistance compared to oxide ceramics, mainly alumina, so research on their manufacturing methods and their applications is ongoing. Recently, it has been widely used, and its application is opening up to high-temperature materials such as heat-resistant structural materials for gas turbines, diesel engines, heat exchangers, etc. that operate at high temperatures. Silicon carbide as a high-temperature material has excellent oxidation resistance, strength properties, and thermal conductivity at high temperatures. Silicon nitride also has excellent thermal shock resistance, coefficient of thermal expansion, fracture toughness, and the like. For this reason, the development of composite ceramics as a new material that incorporates the advantages of both has been progressing recently. Such silicon nitride and silicon carbide are mainly processed and formed by sintering, but important factors to obtain a high-density sintered body include the composition, purity, and
Examples include crystal type, particle size, particle shape, etc. Non-oxidizing silicon-based ceramics are generally difficult to sinter, and therefore, raw material powder with excellent sintering properties is particularly required to have submicron-level particle diameters and be uniform. Conventionally, the following methods are known as main methods for producing single silicon nitride products. (1) A method of nitriding metallic silicon powder by heating it to high temperatures in nitrogen or ammonia gas. (2) A method of simultaneously reducing and nitriding a mixture of silica powder and carbon by heating it to high temperatures in nitrogen. (3) An amide or imide thermal decomposition method in which silicon tetrachloride and ammonia are reacted at room temperature or low temperature, the resulting silicon amide or silicon imide is separated, and then heated to a high temperature in a nitrogen or ammonia atmosphere. (4) A method in which silicon tetrachloride and ammonia undergo a gas phase reaction at high temperatures. However, each of these methods has the following problems that must be solved. Regarding (1), although this method is currently used industrially, it is difficult to obtain a fine powder, and the product obtained by this method needs to be pulverized for a long time. For this reason, impurities such as Fe, Ca, Al, etc. contained in the raw Si material remain even after nitriding, or impurities are mixed in during the pulverization process. Method (2) not only requires the use of sufficiently purified silica powder and carbon powder as raw materials, but also the resulting products are α-type Si ₃ N ₄ , β-type Si ₃ N ₄ ,
It is a mixture of silicon oxynitride, etc., and it is difficult to reduce particle size and variation in particle size. Method (3) includes a liquid phase method and a gas phase method, but in both methods, a large amount of ammonium chloride is produced as a by-product along with silicon amide and silicon imide. Therefore, it is troublesome to separate the product and remove ammonium chloride in the thermal decomposition step, and corrosion or contamination with impurities due to the use of a solvent is likely to occur. Furthermore, there are limits to the particle size and crystal type of powder obtained by thermally decomposing silicon amide or silicon imide, making it possible to form fine particles or regular equiaxed granules. Among these, the gas phase method (4) is said to yield high quality products. However, since the reaction between silicon tetrachloride and ammonia is fast, the reaction also occurs at the outlet of each raw material gas supply pipe, which not only blocks the outlet and makes long-term continuous operation impossible; There is the trouble of removing the by-product ammonium chloride, and measures must be taken to prevent corrosion of the equipment. Furthermore, even if ammonium chloride is completely removed, trace amounts of chlorine are difficult to remove, and silicon nitride may turn into β-crystals in the subsequent crystallization process, or the crystal form may become acicular, which may have an adverse effect on sintering. It begins to affect people. Furthermore, the following methods have been known as main methods for producing silicon carbide alone. (1) A method in which silica stone (SiO ₂ ) and coke (C) are mixed and heated in an Acheson furnace. (2) Solid phase reaction method of metallic silicon powder and carbon powder. (3) Solid phase reaction method between silica powder and carbon powder. However, both methods have drawbacks such as non-volatile metal impurities contained in the raw materials, which may accumulate in the product, or make it difficult to reduce particle size variation. It was hot. The individual powders of silicon nitride and silicon carbide obtained by the above manufacturing method are molded and sintered by various commonly known methods such as hot pressing, pressureless sintering, and reaction sintering. Various methods for manufacturing composite sintered bodies that incorporate the advantages of both silicon nitride and silicon carbide have been studied, and for example, the following manufacturing methods are known. (1) A method in which silicon nitride and silicon carbide powder are mechanically mixed, molded using a hot press, etc., and sintered. (2) Using a reaction sintering method, a mixture of silicon carbide and silicon is formed in advance and then a nitriding reaction is performed to generate silicon nitride, or a mixture of silicon nitride and carbon is formed and then silicon is formed. A method of infiltrating and producing silicon carbide. (3) A method in which an organic silicon polymer is used as a raw material, silicon powder is added thereto, the polymer is molded either directly or after heat treatment, and a nitriding reaction is performed to produce silicon carbide and silicon nitride. However, in these attempts, there is a limit to the ability to sufficiently control the particle characteristics such as particle size and shape, as well as the degree of mixing, and to mix each component uniformly by using ordinary raw material powder. mechanical grinding,
Since impurities are likely to be mixed in by mixing, a desirable sintered body cannot be obtained. In addition, even the reaction sintering method has drawbacks such as increased porosity, complicated processes and operations, and limited uniformity of composition, making it impossible to obtain a desirable sintered body. The present inventors have conducted extensive research on various methods for synthesizing fine powders of silicon nitride and silicon carbide in order to obtain a composite sintered body of silicon nitride and silicon carbide with excellent high-temperature properties. As a result, by controlling the reaction conditions when reacting a specific organosilicon compound in the gas phase and obtaining a fine composite powder of silicon nitride and silicon carbide, a sintered body with excellent high-temperature properties as described above can be produced. The present invention was completed based on the discovery that the following can be obtained. That is, in the present invention, the general formula is [R ¹ , R ² , R ³ Si] ₂
NR ⁴ , or [-R ¹ , R ² , Si-NR ³ ]-n (wherein R ¹
~ ^R4 is hydrogen, alkyl group, allyl group, respectively
A silazane compound represented by a phenyl group, a methylamino group, etc., and n is 3 or 4) is uniformly mixed with ammonia and/or an inert gas and supplied to the reaction zone before being subjected to the reaction. Raw material gas partial pressure, reaction time, i.e. 0.01~0.5atm
A method for producing a composite fine powder consisting of crystalline silicon nitride and silicon carbide, characterized in that the composite fine powder obtained by reacting in the gas phase for 60 to 0.1 seconds is heat-treated at 1400 to 1600°C. It is. According to the method of the present invention, a fine composite powder containing silicon nitride and silicon carbide uniformly on the order of fine particles of 1 micron or less can be easily obtained. Next, the present invention will be explained in detail. In the present invention, Si, N, C used as raw materials
and H, the general formula is [R ¹ , R ² , R ³ Si] ₂ NR ₄ or [-R ¹ , R ² , Si-
NR ³ ]-n (in the formula, R ¹ to ^{R 4} each represent hydrogen, an alkyl group, an allyl group, a phenyl group, a methylamino group, etc., and n is 3 or 4), such as [HSi(CH ₃ ) ₂ ] ₂ NH, [(CH ₃ ) ₃
Si] ₂ NH, [(CH ₃ )Si] ₂ NCH ₃ , [(CH ₂ =CH)Si
(CH ₃ ) ₂ ]NH, [−(CH ₃ ) ₂ Si−NH]− ₃ , [−
(CH ₃ ) ₂ Si-NCH ₃ ]- ₃ or a 6-membered cyclic tris(N-methylamino) tri-N-methyl- having a methylamino group as a device group on silicon, as shown by the following structural formula: cyclotrisilazene and the like. These raw materials may be used as a mixture of two or more types as required, and hydrocarbons may also be used together. When these raw materials are in a liquid or solid state at room temperature, these raw materials are supplied to the reaction zone by means such as appropriate indirect heating in order to quickly carry out a uniform reaction and obtain the desired composite powder. This allows the raw material to be gasified and mixed uniformly with ammonia and/or inert gas, or the raw material silicon compound to be gasified and ammonia and/or inert gas to be uniformly mixed and supplied to the reaction zone. It is important to obtain composite fine powder. In addition, as shown in the examples, the raw materials are NH ₃ , H ₂ ,
By entraining non-oxidizing gases such as N ₂ , Ar, He, etc., it is possible not only to adjust the raw material partial pressure and control the supply rate, but also to entrain NH ₃ ,
The composition of _the produced powder (SiC _, Si ₃ N ₄
ratio) can be controlled arbitrarily. For example, if you want to increase the proportion of Si ₃ N ₄ ,
It is effective to increase the amount of NH ₃ and H ₂ , but
The required amount varies depending on the type and concentration of the silicon compound, reaction temperature, reaction time, etc. The partial pressure of the raw material gas during the reaction period and the reaction time are determined by the particle size and shape of the product, the space-time yield, etc.
A range of degrees is preferred. The reaction time is generally
Although it can be carried out in a wide range of 120 to 0.0.5 seconds, a range of 60 to 0.1 seconds is suitable to obtain a uniform fine powder. If the reaction partial pressure is smaller than these values or the reaction time is longer, the reactor will become unnecessarily large, which is disadvantageous from an industrial perspective; conversely, if the reaction partial pressure is larger than these values, If the reaction time is too short, the reaction may not substantially proceed, which is not preferable. Further, the reaction temperature is generally in the range of 600 to 1600°C, preferably 800 to 1500°C. If the temperature is lower than 600℃, the reaction will not proceed sufficiently and the production rate of silicon nitrides and carbides will be low;
If the temperature exceeds 1600°C, a large amount of energy is required, so it is not economical. As a specific means of carrying out the method of the present invention, for example, the organic silicon compound as a raw material is gasified in advance and, if necessary, thoroughly and uniformly mixed with ammonia and non-oxidizing gases such as H ₂ and N ₂ . After that, it is introduced into an externally heated reaction tube. The reaction tube used is either an empty column or a packed column type, but it is important to have a structure that prevents the gas flow from becoming pulsating or turbulent and maintains thermal uniformity. Important for powder uniformity. The generated gas containing silicon nitrides and carbides is cooled and introduced into a collection device, but the collection device used in the present invention is not particularly limited and can be any commonly used packed bed type or filtration type dust collector. , electrostatic precipitator,
A cyclone, etc. can be used as appropriate, but since the generated gas does not contain hydrogen chloride, a corrosive gas, or ammonium chloride, which becomes solid and precipitates when cooled to below 500°C, Since it does not require the use of materials or processing equipment to remove ammonium chloride, an economical collection method can be selected. The amorphous composite powder obtained in this way can be fed as it is to the molding and sintering process, but it is chemically unstable and gas is easily generated during sintering. May cause defects in the body. For this purpose, the obtained amorphous fine powder is further heat-treated at 1200 to 1700°C, preferably 1400 to 1600°C in a non-oxidizing gas atmosphere to stabilize and crystallize it. The time for this heat treatment varies depending on the composition of the composite powder, the degree of crystallization, etc., but is usually about 0.5 to 5 hours. As shown in the photographs in the drawings, the obtained composite fine powders all have a particle size of 1 micron or less,
Moreover, it has a uniform particle size distribution. EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to these Examples. Examples 1 to 6 A device consisting of a high-purity alumina reaction tube with an inner diameter of 25 mm and a length of 700 mm installed in an electric furnace and a reaction product collector attached to the outlet of the reaction tube was used to reach a predetermined reaction temperature. held. After the silazane compound was gasified, it was thoroughly mixed with ammonia and non-oxidizing gas N ₂ or H ₂ gas, and the mixture was blown into the inlet of the reaction tube to cause a reaction. All of the fine powders collected in the collector were equiaxed, uniform fine particles with a particle size of 1 micron or less. A scanning electron micrograph of the collected fine particles obtained in Example 3 is shown in FIG. Next, this product was filled into a high-purity alumina tube under an inert atmosphere, and heat-treated for 2 hours in an electric furnace heated to 1500°C under an argon atmosphere. The reaction conditions and analysis results of the obtained powder are shown in Table 1, and in both cases, β-sic and α-Si ₃
There was only _N4 component. In addition, when impurities were measured using fluorescent X-ray analysis, the content of Fe, Al, Ca, and Ka was less than 10 ppm each, and the content of Cl was less than 10 ppm.
It was less than 100ppm.

【table】

【table】 [Brief explanation of the drawing]

Since it is not possible to show the particle structure of the composite fine powder using a drawing, FIG. 1 is a scanning micrograph showing the structure of powder particles.

Claims (1)

[Claims] 1 The general formula is [R ¹ , R ² , R ³ , Si]NR ⁴ or [-R ¹ , R ² , Si-NR ³ ]-n (wherein R ¹ to ^{R 4} are hydrogen and alkyl groups, respectively) , allyl group, phenyl group, methylaminomethyl group, etc., and n is 3 or 4) is uniformly mixed with ammonia and/or an inert gas before being subjected to the reaction, and then added to the reaction zone. The composite fine powder obtained by reacting in the gas phase at a raw material gas partial pressure of 0.01 to 0.5 atm and a reaction time of 60 to 0.1 seconds is 1400 to 1600
A method for producing a composite fine powder consisting of crystalline silicon nitride and silicon carbide, characterized by heat treatment at ℃.