JPS60195099A - Production of silicon nitride whisker - Google Patents

Abstract

PURPOSE:To produce silicon nitride whisker having an a-type crystal structure, in high yield, by dissolving silicon tetrachloride in a large amount of an organic solvent, passing ammonia gas thereto, and thermally decomposing the produced silicon diimide under a specific condition. CONSTITUTION:Silicon tetrachloride is dissolved in >=10 times vol., preferably about >=20 times vol. of an organic solvent such as n-hexane, and ammonia gas is passed through the solution while cooling the solution at about 0 deg.C. The produced silicon diimide is collected by evaporating the solvent. The silicon diimide is heated in a mixed gas stream composed of ammonia gas and/or nitrogen gas and hydrogen gas at a temperature increase of <=450 deg.C/hr to evaporate the remaining solvent, ammonium chloride, etc. successively, and then heated at 1,300-1,450 deg.C for >=2hr to remove the existing chlorine ion and oxygen, etc. completely, and to effect the thermal decomposition of the diimide to the silicon nitride whisker having an a-type crystal structure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves the manufacturing conditions of silicon nitride and thereby increases α
The present invention relates to a method of manufacturing whisker-like silicon nitride having a -type crystal structure.

Oxide-based materials have conventionally been the mainstream as ceramic materials, but recently silicon carbide and silicon nitride have been attracting attention. Among these, silicon nitride (for example, SN, N4), which is the subject of the present invention, has high expectations as a heat-resistant structural material because of its excellent high-temperature strength, abrasion resistance, and corrosion resistance. On the other hand, various methods are being explored for producing silicon nitride, but α- is the most suitable as a raw material for sintered bodies.
It is said that the α-type crystal content is high.
Thermal decomposition of silicon diimide is attracting attention as a method with a high generation rate of type crystals. The present inventors have also been researching the thermal decomposition method of silicon diimide for some time, and have considered ways to further increase the production ratio of α-type crystals and create whisker-like crystals that are more suitable as high-strength materials. The present invention has been completed as a result of these efforts, and its purpose is to provide a method for producing whisker-like silicon nitride having an α-type crystal structure with good yield. The method of the present invention that meets the above objective is a method for producing silicon nitride by dissolving silicon tetrachloride in an organic solvent, passing ammonia gas through it, and then thermally decomposing the silicon diimide produced. 1) The amount of organic solvent used is 10 times or more (volume ratio) to the amount of silicon tetrachloride used, (2) The thermal decomposition reaction is carried out using gas selected from the group consisting of ammonia gas and nitrogen gas. (3) The heating temperature increase rate in the pyrolysis reaction is 45%.
(4) The heating conditions for thermal decomposition should be 1800 to 1450°C.
The gist lies in fulfilling the following four conditions: , 2 hours, and above.

The reason why we decided to use an organic solvent with a volume more than 10 times that of silicon tetrachloride is to make the crystal grains of silicon diimide formed by the reaction between silicon tetrachloride and ammonia gas and ammonium chloride, which is a by-product, fine. At the same time, by dispersing it in an organic solvent, it not only serves as a high-quality raw material for the next thermal decomposition reaction, but also prevents the ammonia gas supply line from being blocked by the product, making the reaction efficient and safe. This is because we believe that it is essential for achieving this goal. The preferred amount of organic solvent used is 4
It has a capacity more than 20 times that of silicon chloride. As the organic solvent, an inert solvent such as n-hexane is generally used, but any other solvent that dissolves silicon tetrachloride and does not adversely affect the progress of the reaction can be used in the present invention. The reaction is usually carried out by introducing ammonia gas while cooling to around 0° C. and bringing about gas-liquid contact.

At the completion of the reaction, it is in the form of a slurry, and it is desirable to isolate silicon diimide, the main product, as pure as possible before the next thermal decomposition reaction.

For this purpose, the organic solvent and unreacted silicon tetrachloride are first separated by distillation, but this operation is preferably carried out in a nitrogen-rich gas atmosphere in order to prevent oxidative decomposition of the silicon diimide. The residue after distillation contains ammonium chloride in addition to silicone diimide, as well as organic solvents remaining due to adsorption, etc., so this is charged into a pyrolysis device and the temperature is gradually raised. It is necessary to remove them one by one.

Therefore, in the present invention, the temperature increase rate during thermal decomposition is set to 450℃/
A slow speed of less than 1 hour is set to first remove the adsorbent solvent and then remove the ammonium chloride.

To give an example of the heating conditions when using n-hexane as a solvent, for example, n-hexane increases in about 30 minutes at a temperature of 150°C.
- Hexane is removed almost II, and further 300-400
When heated to ℃, ammonium chloride sublimates. In addition to the above impurities, there are chlorine ions and oxygen, and in order to remove these, it is necessary to start thermal decomposition under the formation of a hydrogen-containing gas flow as described below, but in any case, 45
If the temperature is raised at a rate exceeding 0°C/hour, the various impurities mentioned above will not be removed sufficiently, and the sinterability of the produced silicon nitride will deteriorate, inhibiting the high temperature strength from being sufficiently increased. However, it is impossible to achieve the desired purpose because the gradual growth of the whiskers cannot be promoted.

It is well known that the thermal decomposition reaction is carried out in a mixed gas flow of ammonia gas and nitrogen gas, whereby chlorine ions coexisting with silicon diimide are removed as ammonium chloride. However, according to the research of Nagisa et al., it was found that when the coexisting oxygen as an impurity is not sufficiently removed, the mechanical properties of the sintered product are adversely affected. Therefore, when hydrogen gas was mixed into the air stream as described above for the purpose of removing oxygen, it was found that oxygen was removed as H,0 and chlorine ions were also removed as HCI. In addition, as a result of the expected effects of hydrogen gas, the combination of ammonia gas and nitrogen gas that previously required the use of (1) snoring gas of ammonia gas and hydrogen gas, and (2) nitrogen gas and It has become clear that either a mixed gas of hydrogen gas or (3) the above-mentioned champion mixed gas may be used. It is recommended that hydrogen gas be mixed in a ratio of 1 to 50 volumes, preferably 5 to 40 volumes.

Finally, regarding the thermal decomposition temperature conditions, if it is less than 1300°C or less than 2 hours, it will be difficult for silicon nitride to crystallize and it will become amorphous, and even if it crystallizes, it will remain as a powder. The whisker-like growth becomes insufficient.

The preferred range of conditions is 1300 to 1450°C for 2 to 6 hours.

Next, Examples and Comparative Examples will be given to clarify the effects of the present invention.

Example 1 201 m of silicon tetrachloride was added to 10,100 O of n-hexania, and the mixture was cooled to 0°C. By passing dry ammonia gas at 7001 nl/min while maintaining the same temperature,
Manufactured silicon diimide. A slurry-like product in which silicon diimide and ammonium chloride were dispersed was subjected to distillation to recover n-hexane, and the distillate was charged into an electric furnace.

Add 400 mJ of mixed gas (amsonia gas: 10 volumes, nitrogen gas: 280 volumes, hydrogen gas: 10% by volume) to this.
The temperature was raised at a rate of 200° C./hour while flowing at a flow rate of 1,400° C./minute, and when the temperature reached 1,400° C., the temperature was maintained for 2 hours to complete the thermal decomposition reaction of silicon diimide. The scanning electron micrograph of the product obtained by cooling is shown in Figure 1, and the X-ray diffraction results are shown in Figure 2, which confirmed that it was a whisker-like S, i, N, rich in α-type crystals. It was done. According to the analysis results, the Si yield was 92% by weight based on the raw material.

Furthermore, Mg0 (5 parts by weight) was added as a sintering aid to quartz crystal (95 parts by weight), and 300 kg, 4 m'', 175
Hot pressing was performed under pressure conditions of 0° C. and 100 minutes to obtain a plate-shaped sample. On the other hand, commercially available powdered Si3N4 was obtained and hot-pressed under exactly the same conditions to obtain a plate-shaped sample. The density and bending strength of these were measured and were as shown in Table 1.

As can be seen in Table 1, the specimen of the present invention exhibited extremely high bending strength, 1.3 times that of the conventional product at room temperature, and 12
It can be seen that the strength is 1.6 times lower at 00°C, and that the high-temperature strength in particular has been dramatically improved.

Example 2 A mixture of silicon diimide and ammonium chloride obtained in the same manner as in Example 1 was heated at 300°C/hour while flowing a mixed gas (ammonia gas = 10 volumes, hydrogen gas 220 volumes) at a rate of 200 mJ/min. The temperature was raised at a rate of 1350
When the temperature reached °C, the temperature was maintained for 4 hours to complete the thermal decomposition reaction of silicon diimide. A scanning electron micrograph of this product is shown in FIG. 3, and the results of X-ray diffraction are shown in FIG.

It can be seen that it is a whisker-like 51 g N4 rich in a-type crystals. When we compared crystal and commercially available powdered 5i6N4 and examined nine impurity analyzes and crystal compositions, we found that the products of the present invention had fewer impurities and an extremely high ratio of α-type crystals, as shown in Table 2. Ta.

Table 2 □ □ Example 3 A mixture of silicon diimide and ammonium chloride obtained in the same manner as in Example 1 was charged with a mixed gas (nitrogen gas
The temperature was raised at a rate of 400°C/hour while flowing hydrogen gas (230 volumes) at 400 d/min, and when it reached 1400°C, it was held for 2 hours to complete thermal decomposition. A scanning electron micrograph of the obtained product is shown in FIG.

Comparative Example 1 60d of silicon tetrachloride was added to 400++J of n-hexane, and while cooling to around 10°C, 70011L of mixed gas (ammonia gas = 95 volumes, hydrogen gas = 5 volumes, q6) was added.
It was allowed to pass under the conditions of 1Z. However, after about 10 minutes, the supply line for the mixed gas was blocked, making it impossible to continue the reaction. At this point, silicon in the n-hexane was measured and the reaction rate was found to be 6°. This seems to be because the amount of organic solvent was too small.

Comparative Example 2 A mixture of silicon diimide and ammonium chloride obtained in the same manner as in Example 1 was charged into an electric furnace and heated under vacuum (1o1~
The silicon nitride was heated at a temperature increase rate of 200°C/hour while maintaining the temperature at 1400"C- (104+<gA+F), and held for 2 hours when the temperature reached 1400"C-. As shown in the X-ray diffraction results (Fig. 7), most of the particles were powdered and β-type crystals appeared, so the object of the present invention could not be achieved. This seems to be because I didn't do it properly.

Comparative Example 3 A mixture of silicon diimide and ammonium chloride obtained in the same manner as in Example 1 was charged into an electric furnace, and a mixed gas (nitrogen gas: 95 volumes, hydrogen gas: 5 volumes) was heated at 400 mJ.
The mixture was heated at a heating rate of 600° C./hour under the condition of 1,350° C./hour without running a sink, and when the temperature reached 1350° C., it was held for 2 hours. The obtained 5i6N4 had an almost perfect powder form as shown in FIG. 8 (scanning electron micrograph). This seems to be because the temperature increase rate was too fast.

[Brief explanation of the drawing]

Figure 11 is a scanning electron micrograph, and Figure 2.4.7 is a graph showing the results of X-ray diffraction. Applicant: Kobe Steel, Ltd. Figure 3 Figure 7 Procedures-? tgj j [-machi-2 (method) % formula %] 2. Name of the invention Process for producing whisker-shaped silicon nitride 3. Person making the amendment 1. Relationship to the matter Patent applicant Wakihama-cho-1, Chuo-ku, Kobe City 'l'l No. 3 No. 18 (1,
19) Kobe Steel Co., Ltd. Representative: Fuyuhiko Maki 4, Agent: Shinko Building, 2-3-7 Dojima, Kita-ku, Osaka 530 June 26, 1980 (Shipping date) 6. Each column of “Detailed Description of the Invention” and “Brief Description of Drawings” as well as Drawing 7 and contents of amendments. (1) The following sections in the statement will be corrected. (a) Page 8, lines 2-3 (Incorrect) The product is as shown in (Correct) The X-ray diffraction results of the product are shown in Figure 1 (Reference photo l is (scanning electron micrograph), (b) Page 9, lines 11-12 (incorrect) of the product. (Correct) The X-ray diffraction results of the product are shown in FIG. 2 (Photo 2 is a scanning electron micrograph). (c) Page 10, Table 2, rows 7-8 from the bottom (wrong) Completed. ...shown below. (Correct) Completed (Reference photo 3 is a scanning electron micrograph). (d) Page 11, lines 11-12 (erroneous) Scanning electron... As shown. (Correct) As shown in the X-ray diffraction results in Figure 3 (Reference photo 4)
(scanning electron micrograph), (e) Page 12, lines 3 to 5 (erroneous) No. 814... (Stop) It was almost completely powdery (Reference photo 5 is a scanning electron fI micrograph). (f) Page 12, lines 7-9 (wrong) 1st, 3rd. It is... (Correct) Figure 1.2.3 is a graph showing the results of X-ray diffraction. . (2) Of the drawings, drawings 1.3, 5, and 6.81M will be deleted as if they were red in the respective copies. Also, as I wrote in red, Figure 2 is stamped on Figure 1, Figure 4 is stamped on Figure 2, and Figure 7 is stamped on Figure 3. We will also submit new reference photos 1 to 5 as shown in the attached sheet.

Claims (1)

[Scope of Claims] A method for producing silicon nitride by dissolving silicon tetrachloride in an organic solvent, passing ammonia gas therein, and then thermally decomposing the produced silicon diimide, which satisfies the following conditions. A method for producing whisker-like silicon nitride, characterized by: The amount of organic solvent used should be at least 10 times (by volume) the amount of silicon tetrachloride used, and the thermal decomposition reaction should be carried out with one or more gases selected from the group consisting of ammonia gas and nitrogen gas. It should be carried out in a mixed gas flow with hydrogen gas, the heating temperature increase rate in the thermal decomposition reaction should be 450°C/hour or less, and the heating conditions in the thermal decomposition should be 130.0 to 1450°C, 2
It should be more than an hour.