JPS59174506A - Manufacture of new powdered silicon nitride - Google Patents

Abstract

PURPOSE:To manufacture high-purity silicon nitride in good yield by collecting a product obtained by reacting a volatile silicon compd. with a decomposable nitrogen compd. contg. no oxygen in a hot air current, on a vanishing filter material. CONSTITUTION:A vanishing filter material 7 (fibrous carbon, powdered silicon dioxide etc.) is provided in a furnace consisting of a refractory furnace wall 4, a heating element 5 and an outer wall 6. The inside of the furance is filled with an inert gas atmosphere and kept at 900-1,400 deg.C. Then a decomposable nitrogen compd. such as ammonia or hydrazine contg. no oxygen from a duct 1 and a volatile silicon compd. such as SiCl4, HSiCl3 and SiF4 from a duct 2 are introduced into the furnace in a 1.5-6 ratio of N/Si (formula weight ratio) to react with each other. The obtained powdered silicon nitride is collected on the filter material 7. (symbol 3 is a gaseous by-product discharging duct) Then the silicon nitride is taken out together with the filter material 7 which is vanished by means of calcination etc. to obtain the high-purity powdered silicon nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a novel method for producing silicon nitride powder, and more specifically, a volatile silicon compound and a decomposable nitrogen compound that does not contain oxygen are brought into contact with each other in a hot air stream to form a silicon nitride powder on a fugitive furnace material. α-type silicon nitride powder, which is a method for producing silicon nitride powder characterized by precipitation and collection, is promising as a high-temperature material because its sintered body has excellent high-temperature strength.

Traditionally, silicon nitride powder has been produced by pulverizing the product obtained by directly nitriding metallic silicon with nitrogen or ammonia, by reducing and nitriding a mixture of silicon dioxide powder and carbon powder in a nitrogen or ammonia atmosphere, or by combining volatile silicon compounds with It has been produced by methods such as direct reaction of ammonia or thermal decomposition of silicon imide. Among these methods, synthesis by direct reaction in a gas phase is a method for obtaining fine silicon nitride powder with a relatively uniform particle size and high purity. However, the disadvantage of direct synthesis in the gas phase is that the yield is very poor. The reason for this is that the product is scattered without being collected, and the raw material is scattered without being reacted.The present invention was made in consideration of this point, and the yield was lower than that of the conventional method. 40-50%,
This is a dramatic improvement of 90%.

That is, although the present invention is generally stated in the claims, scattering of the product can be prevented by using a fugitive furnace material.
Furthermore, the issue of dissipation of unreacted raw materials has been solved by using specific contact conditions. To explain the contact conditions of the raw materials first, the volatile silicon compound and the decomposable nitrogen compound that does not contain oxygen have a N/Si (formulaic ratio) of 900 to 1400, with the stoichiometric ratio of silicon nitride being 4/3 or more. This is done in a hot air stream at ℃.

At temperatures below 900° C., silicon imide is produced which easily decomposes in the air to form 5i02.

If the temperature exceeds 1400° C., there will be no particular advantage except for the problem of material selection.

Here, N/Si (formula weight ratio) is carried out at 4/3 or more, but it is even better to have a trench ratio in the range of 1.5 to 6. The reason is that N/S'i is 1.5 or less. This is because unreacted volatile silicon compounds are discharged out of the system, and when N/Si exceeds 6, there is only a mere loss of ammonia and hydrazine.

It is convenient to use a furnace when contacting the raw materials in a hot air stream. Furnace as referred to herein means a refractory reaction vessel provided with an exhaust outlet for by-product gases. The inside of such a furnace is easily heated to 900 to 1400° C. and creates a reducing atmosphere, which is advantageous for producing silicon nitride.

The volatile silicon compound and the decomposable nitrogen compound that does not contain oxygen may be charged into the heated furnace either individually or simultaneously as a mixture.

In the present invention, the volatile silicon compound has the general formula 5i) (4
In this formula, X is hydrogen, a halogen atom, or an alkyl group. Specific examples of silicon compounds include 5iCt4, H5iCA3, SiH4, Si(CH3
)4, (CH3)2 St C1z, CH35iCt3
, SiF4, etc., or a mixture thereof may be used.

Examples of decomposable nitrogen compounds that do not contain oxygen include ammonia and hydrazine.

In addition, the fugitive furnace material in the present invention refers to materials that are stable at high temperatures and have a high surface area, such as fibrous carbon, carbon black, and silicon dioxide powder, but that disappear later by incineration or washing with hydrofluoric acid. It is something that can be done. The reason why silicon nitride is precipitated and collected using such a fugitive furnace material is that most of the silicon nitride produced in the present invention is amorphous, so a specific heat treatment for which a separate patent application has been applied is applied to convert it into α-type. Since it is necessary to convert it into crystals, the object of the present invention will not be hindered as long as it can be easily eliminated during or after this treatment.

That is, in the case of fibrous carbon, carbon black, etc., it can be removed by incineration in an oxidizing atmosphere2, and in the case of silicon dioxide powder, etc., it can be removed with hydrofluoric acid.

Example-1 The reactor shown in the drawing (inner diameter 50 mm, length 1 m) was used. Fibrous carbon was installed in the reactor as a fugitive reactor material (7), and the inside of the reactor was set as an inert gas atmosphere.
The temperature was raised to ℃. After that, ammonia gas (70mA/m1n) was supplied from duct (1), and 5iCt4 was supplied from duct (2).
(0.32 L/min) was reacted for 2 hours to obtain silicon nitride powder of the present invention.

The silicon nitride powder precipitated and collected on the fibrous carbon is coarsely pulverized together with the fugitive p-material and converted into α-type silicon nitride powder under specific conditions.
It was baked at 0°C to remove fibrous carbon. The obtained silicon nitride had high purity and relatively uniform particle size. The yields based on silicon are summarized in the table below.

Example 2 A carbon blank was used as the fugitive furnace material, the inside of the furnace was kept at a pressure lower than atmospheric pressure in an inert gas atmosphere, and heated to 1300°C. At that temperature, ammonia (50ml/min
), 5iF4 (0.14 f/m1n) were introduced into the reaction system, and the reaction was carried out for 3 hours while maintaining the system pressure at 30 torr to obtain the silicon nitride powder of the present invention.

This material was coarsely pulverized together with the fugitive furnace material, then crystallized into the α-type under specific conditions, and the carbon black was then removed by incineration in the air to obtain α-type silicon nitride powder.

Example-3 SiO+ powder was used as the fugitive furnace material, and ammonia (6
0m/L/m1n) and CH35iC41 (0, 25f/
The reaction was carried out for 2 hours in the furnace shown in the drawing with the temperature (min) set at 1200° C. to obtain silicon nitride powder. The obtained product was coarsely pulverized as it was and crystallized into the α type. Only psiO2 of 5i02 mixed in this material was removed with hydrofluoric acid to obtain silicon nitride.

Example-4 Using carbon black as the fugitive E material, the inside of the furnace was heated to 11
Heated to 00℃, 5iCt4 (0-34f/m1n),
Hydrazine (5, I P/min) was introduced and the reaction was carried out for 2 hours to obtain silicon nitride powder. This material was converted into α-type silicon nitride through a specific treatment, and carbon black was further removed by incineration at 800° C. in air.

Comparative Example-1 5iC4 (0,3
9f/min) and ammonia (75mt/min
) and reacted for 2 hours to form silicon nitride powder (6,
422) was generated. (This method is a conventional method.)
The silicon nitride obtained was amorphous with a purity of 99.4% and a specific surface area of 10.7 m2/l, but the yield was extremely low at 50.2%. .

The following table summarizes the main points of the above results.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a furnace used in carrying out the present invention. In the figure, 1 and 2 are ducts for charging raw materials, 3 is a duct for discharging by-product gas, 4 is a refractory furnace wall, 5 is a heating element, 6 is an outer wall, and 7 is a fugitive p material. Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1) A novel method characterized in that a volatile silicon compound and a decomposable nitrogen compound not containing an enzyme are brought into contact with each other in a hot air stream to precipitate and collect a reaction product on a fugitive reactor material. Method for manufacturing silicon nitride powder. 2) The method according to claim 1, characterized in that the temperature of the hot air stream is 900° C. to 14,000° C. 3) The quantitative ratio of the volatile silicon compound and the oxygen-free decomposable nitrogen compound to be brought into contact is 1.5 to 6 as the formula weight ratio N/Si.
The method according to claim 1 or 2, characterized in that: