JPS6132244B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing silicon nitride powder,
In particular, it is intended to propose developments relating to an advantageous reduction in the content of halogens and oxygen. Silicon nitride is useful for its excellent heat resistance and corrosion resistance, and is used for various purposes. In recent years, the application of high-temperature materials such as gas turbines has received particular attention, and the demand for high-purity and fine silicon nitride powder as a raw material is especially strong. It has come to be. Conventionally, methods for producing silicon nitride powder include (1) directly nitriding metal silicon powder, (2) reducing silica powder with graphite powder and nitriding it, and (3) reacting silicon halide with ammonia. There are several methods for producing silicon nitride powder, and the last method is particularly excellent as a method for producing silicon nitride powder with less metal impurities. This method is further divided into (a) a method in which the reaction is carried out near room temperature or at a low temperature, and (b) a method in which the reaction is carried out at a high temperature. The reaction product obtained by the low temperature method (a) is silicon imide.
It is a nitrogen-containing silane compound represented by Si(NH) ₂ and its ammonia adduct, and silicon nitride powder with low halogen content can be easily obtained by heat treatment in a nitrogen or ammonia atmosphere. On the other hand, a large amount of halogenated ammonium is produced as a by-product during the reaction, which must be removed by heat treatment, which greatly reduces the volumetric efficiency of the furnace, and also prevents ammonium halides from forming in the low-temperature section of the furnace. It has the disadvantage of redepositing and clogging the furnace. On the other hand, in the high-temperature method (b), gaseous hydrogen chloride is produced as a by-product, and the ammonium halide does not cause any adverse effects or can at least significantly reduce the harmful effects, and such reaction products are not the same as in the case of (a). Silicon nitride powder can be obtained by heat treatment in the same manner. At this time, the atmosphere for heat treatment is nitrogen and/or
Alternatively, it is known that the reaction is carried out in ammonia, but unlike the nitrogen-containing silane compound obtained by the low-temperature method (a), there is a halogen directly bonded in the reaction product. Therefore, this halogen cannot be removed by heat treatment in nitrogen, which has a negative effect on sintering properties.In addition, it is difficult to crystallize to form α-silicon nitride powder, and furthermore, when trying to remove the halogen, it is difficult to remove the halogen. If heat treatment is performed at a high temperature and/or for a long time, the silicon nitride powder will become β crystallized, making it unsuitable as a raw material for a sintered body. However, if heat treatment is performed in ammonia, even if halogens can be removed, the ammonia will corrode furnace materials such as alumina and mullite, reducing the lifespan of the furnace materials and increasing the risk of impurity contamination from the furnace materials. In addition, the silicon nitride powder obtained here has the disadvantage that the silicon nitride powder is easily susceptible to acicular particles, and the oxygen content in the silicon nitride powder increases, resulting in a decrease in the high-temperature properties of the sintered body. However, the drawback of reduced sinterability is also difficult to overlook. The inventors conducted various studies and repeated experiments in an attempt to overcome the unresolved problems in the conventional methods, and as a result, they discovered that silicon halides or hydrogenated silicon halides and ammonia were mixed in a gas phase at 600 to 1500°C. It was discovered that when the reaction product obtained by the reaction is heat-treated in an ammonia-containing gas, the halogen in the reaction product can be removed even at a relatively low temperature that does not cause corrosion of the furnace material. By further heat-treating the dehalogenated reaction product in an inert gas, it is possible to easily alpha-crystallize it at a relatively low temperature that would be difficult to alpha-crystallize with consistent heat treatment in an inert gas alone. In this case, corrosion of the furnace material does not occur when heat treatment is continued in an ammonia atmosphere, and the oxygen content in silicon nitride can also be advantageously reduced. It has been successively discovered that heat treatment alone can greatly suppress the formation of needle-like objects, which are thought to be generated by vapor phase growth involving oxygen. This invention was completed based on these findings, and consists of silicon halide or silicon hydride and ammonia in a molar ratio of 0.1 to 1.85 to the silicon halide in a gas phase at 600 to 1500°C. heating the reaction product obtained by the reaction at a temperature of 100 to 1400 °C in a gas containing at least 20% by volume of ammonia, and then at a temperature of 100 to 1400 °C with at least 50% argon.
Temperature 1000~1650℃ in inert gas containing % by volume
By combining heating at This made it possible. This invention will be explained in detail below. The silicon halides or hydrogenated silicon halides used as starting materials for the method of this invention include SiCl ₄ , SiBr ₄ , Sil ₄ and SiHCl ₃ , SiHBr ₃ ,
SiHI ₃ or SiH ₂ Cl ₂ , SiH ₂ Br ₂ , SiH ₂ I ₂ or
SiH ₃ Cl, SiH ₃ Br, SiH ₃ I as well as SiCl ₂ Br ₂ ,
SiCl ₂ I ₂ and the like, and the reaction between these and ammonia is carried out in the gas phase at a temperature of 600 to 1500°C. Here, silicon tetrachloride, which is liquid or solid at room temperature, is heated appropriately to form a vapor, and if necessary, reacts with ammonia using an inert gas such as nitrogen or argon as a carrier. preferable. If the reaction temperature is too low than 600℃, a large amount of ammonium halide produced during the reaction will accumulate in the low temperature part of the reactor, causing clogging of the reactor, and if it exceeds 1500℃, the rate of thermal decomposition of ammonia will be too fast. This results in a decrease in reaction efficiency. The reaction time is not particularly limited, but since the reaction occurs relatively quickly, it is not necessary to carry out the reaction for a long time. The reaction product thus obtained is heated first in an ammonia-containing gas and then in an inert gas containing at least 50% by volume of argon, and this two-stage treatment is important in view of the purpose of the invention. A specific method is to heat it in an ammonia-containing gas, then switch the atmospheric gas to an inert gas and continue heating. The reaction product, which has been heated in an ammonia-containing gas and dehalogenated, is transferred and heated in a furnace maintained in an inert gas atmosphere. These methods include, but are not limited to, preferred methods from the viewpoint of productivity and prevention of oxidation during transportation. Here, the ammonia-containing gas includes ammonia gas alone and ammonia gas diluted with another gas, and the ammonia content of the diluted gas is at least 20% by volume, with the remainder being nitrogen and/or
Alternatively, argon gas is preferred. If the ammonia content is less than 20% by volume,
No effect on halogen removal was observed. Next, heating in ammonia-containing gas is 100 to 1400
℃ is preferably 500 to 1400℃, more preferably 900℃
Preferably, the reaction is carried out at ~1400°C for 50 hours to 10 minutes.
At temperatures below 100°C, no halogen removal effect is observed, and at temperatures above 1400°C, no improvement in the halogen removal effect can be expected, and moreover, corrosion of the furnace material increases, and the oxygen content in silicon nitride decreases. Not only will the amount increase, but also the generation of needle-like objects will increase. Heating time is 10
If the time is less than 50 hours, the halogen removal effect will not be substantially observed, and even if it exceeds 50 hours, no improvement in the halogen removal effect can be expected, which is uneconomical. Next, the inert gas containing at least 50% by volume of argon in post-heating refers to the case of argon alone and the case of an inert gas containing at least 50% by volume of argon, and in the latter case, the inert gas containing at least 50% by volume of argon is used. Other gases that may be used include nitrogen, helium, and the like. This inert gas tends to shorten the heating time and reduce the oxygen content, compared to, for example, only nitrogen gas. Heating in an inert gas containing at least 50% by volume of argon is preferably carried out at 1000-1650°C for 30 hours to 10 minutes. At temperatures below 1,000°C, the effect of oxygen reduction by this heat treatment is small, and at temperatures above 1,650°C, silicon nitride becomes β crystallized, making it unsuitable as a sintering raw material. More preferably 1400-1650
By heating in the temperature range of .degree. C., a silicon nitride powder with less needle-shaped particles can be obtained, which progresses alpha crystallization, which cannot be achieved by simply consistently performing heat treatment in an inert atmosphere. If the heating time is less than 10 minutes, there will be no oxygen removal effect, and if it exceeds 30 hours, no improvement in the oxygen removal effect can be expected and it will become uneconomical. As explained above, according to the present invention, high purity silicon nitride powder with low halogen and oxygen contents can be obtained, and it is also possible to prevent corrosion of furnace materials such as alumina and mullite. A silicon nitride powder containing α-silicon nitride as a main component and having particularly few needles can be advantageously obtained. When following the method of this invention, the halogen content is
0.5% by weight or less, oxygen content of 3% by weight or less, amorphous or α-crystalline Si ₃ N ₄ , and the production of needles is 20% or less. can be achieved. Here α−Si ₃ N ₄ is
Fixation was performed using a line diffraction method, and needle-like particles were determined by particle shape observation using an electron microscope. The examples listed in the following table will be described below.

[Table] In experiments Nos. 1 to 7, silicon tetrachloride vapor was introduced into the reaction tube at a rate of 73 g/hr and ammonia gas was introduced at a rate of 10 g/hr into the reaction tube, using nitrogen gas as a carrier. The reaction tube was an alumina tube with an inner diameter of 40 mm and a length of 1000 mm, and was maintained at each temperature listed in the table using a vertical tube furnace. The obtained reaction product was collected in a container attached to the bottom of the reaction tube. At this time, gas chromatography analysis of the gas after the reaction revealed the production of hydrogen chloride, while IR analysis confirmed that the reaction product was a powder different from silicon imide. This reaction product was subjected to the next ammonia-containing gas treatment. That is, the reaction product is inserted into an alumina furnace tube, and heated to the specified temperature shown in the table in an electric furnace.
Heating for a given period of time was carried out in a stream of ammonia gas, adjusted to a given ammonia content by dilution with nitrogen gas, or without dilution. Next, the ammonia-containing gas was stopped and replaced with various inert gases shown in the table for replacement, and then an inert gas treatment was carried out under heating at a predetermined temperature and for a predetermined period of time as shown in the table. The oxygen content of the silicon nitride powder obtained by the above two-step heat treatment was measured using a residual analyzer (Reco Co., Ltd.).
RO-18), the chlorine content was determined using the fluorescent X-ray method,
Further, the crystal forms of each were analyzed by X-ray diffraction method. The results are shown in the table. In addition, in the column of product analysis results in the table, those with α/β of 90% or more were classified as α crystal form. In addition, electron micrographs of the silicon nitride powder were taken to observe the particle shape. As a result, the content of needle-like substances was low in all cases. As an example of an electron micrograph, Experiment No. 8 is shown in Figure 1.
In addition, as a result of measuring the area ratio of needles with a length/breadth ratio of 5 or more and granules with a ratio of 5 or less, the content of needles was 20% or less in both cases, as shown in the table. . Experiments Nos. 8 to 9 used SiHCl ₃ and SiBr ₄ instead of hexachloride described above, respectively.
The results of the same procedure as above are listed in the table together with the heat treatment at each stage. Experiments Nos. 10 to 12 are the results of comparative examples in which reaction products obtained in the same manner as Experiments Nos. 1 to 7 were heated under the conditions shown in the table only in ammonia or ammonia-containing gas and nitrogen. shows. In addition, as an example of the results of observing the particle shapes of Experiments No. 10 and 11, Experiment No. 10 is shown in Figure 2. The content exceeded 90%. As described below, according to the present invention, the halogen and oxygen contents are significantly reduced, and α-Si ₃ N ₄
It is possible to advantageously obtain a finely powdered silicon nitride powder mainly composed of silicon nitride and having fewer needles.

[Brief explanation of the drawing]

Figures 1 and 2 show the granular shapes of silicon nitride powders obtained in Experiment No. 8 and Experiment No. 10.
This is an electron micrograph at 6000x magnification.

Claims (1)

[Claims] 1. At least 20% by volume of ammonia is contained in the reaction product obtained by reacting silicon halide or hydrogenated silicon halide with ammonia in the gas phase at a temperature of 600 to 1500°C. Heating at a temperature of 100 to 1400°C in a gas containing
X It is characterized by obtaining a fine powder product that is identified as amorphous or α-crystalline Si ₃ N ₄ by line diffraction, and whose particle shape is determined by electron microscopy and contains 20% or less of needles. A method for producing silicon nitride powder.