JPS59203714A - Manufacture of silicon nitride - Google Patents

Abstract

PURPOSE:To manufacture inexpensively high quality silicon nitride consisting of fine particles and having superior characteristics at high temp. by bringing a mixture consisting of SiO2, C powder and specified additives into a reaction by heating to a high temp. in an atmosphere contg. nitrogen. CONSTITUTION:To 1pt.wt. of SiO2 are added 0.4-2pts. C powder such as carbon black and 0.0001-0.03pt. of one or more kinds of compounds selected among oxides such as LiOH, GeO2, Y2O3, ZrO2, Nb2O5, La2O3, CeO2 and Ta2O5, nitri des such as AlN and ZrN, and composite oxides such as Y3Al5O12 as additives. They are mixed, and the mixture is heated to 1,350-1,500 deg.C in a gaseous nitrogen atmosphere or an atmosphere of a mixture of gaseous nitrogen with <=30vol% gaseous hydrogen. High quality Si3N4 consisting of fine particles and having superior mechanical properties, thermal shock resistance and chemical stability at high temp. can be inexpensively manufactured in a high yield.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing silicon nitride.

Silicon nitride (Six N4) is a sintered body that has excellent mechanical strength, thermal shock resistance, and chemical stability at high temperatures, so it is being actively developed for various uses, and the manufacturing method of silicon nitride itself is being developed. Efforts are also being made to obtain high-purity, high-quality silicon nitride.

Conventionally, various methods for manufacturing silicon nitride have been proposed and studied.

For example, 9 manufacturing methods include:

(1) Method of nitriding metal silicon powder.

(2) A method of thermally decomposing silicon tetrachloride or organic silane in a gas containing total nitrogen.

(3) A method of nitriding a mixed powder of silicon dioxide and carbon or a mixed powder of silicon and silicon dioxide.

and so on.

Among the above-mentioned conventional techniques, method (1) requires a very high price for the raw material powder, so the manufacturing cost of the final product, silicon nitride, is also very high.Also, with this method, it is difficult to obtain high-quality silicon nitride. Have difficulty. What is the method for (2)?

Although silicon nitride can be obtained in relatively high yield.

It is difficult to mass produce, and the raw materials are expensive and production costs are high. On the other hand, method (3) uses silicon dioxide, which is an abundant resource, so the raw material is easily available, mass production is possible, and it is an industrially very advantageous method for producing silicon nitride.

As one of the methods (3), silicon dioxide (SXO,
) as a starting material. In this method, silicon dioxide (Sins) and carbon (0) are mixed to form a raw material powder, and this is heated to a temperature of 1300 to 1500°C in a nitrogen atmosphere to obtain silicon nitride (SimN4)'e. be. However, in this conventional method.

During the synthesis of silicon nitride, the stoichiometric ratio (K=[(!]/(
5j-02) (nol) = 2), it is necessary to use sufficiently purified silicon dioxide powder and carbon powder as the raw materials, and the product is silicon nitride, silicon carbide, silicon dioxide, It is a mixture of silicon oxynitride, etc., and high quality silicon nitride cannot be obtained. In addition, when synthesizing silicon nitride, the stoichiometric ratio (K)
If a much larger excess of carbon (eg K) is added, the rate at which silicon dioxide can be exchanged into silicon carbide increases.

To this extent, a satisfactory silicon nitride can be obtained. but.

Adding excess carbon makes it difficult to synthesize silicon nitride (sbN<) in the presence of excess carbon because this excess carbon will eventually be burned and consumed in the atmosphere.

The manufacturing price becomes high and it becomes industrially disadvantageous,
It is also difficult to obtain high quality silicon nitride with high purity.

Therefore, in view of the above-mentioned conventional problems, the inventors of the present invention conducted various studies and systematic experiments to solve the problems, and as a result, they came up with the present invention.

The purpose of the present invention is to produce high-quality silicon nitride in the form of fine particles--3-
- To provide a method for manufacturing with high yield and at low cost.

That is, 1 the present invention contains 0.4 to 2 parts by weight of carbon powder and lithium hydroxide per 1 part by weight of silicon dioxide.

Additive containing one or more of germanium oxide, yttrium oxide, zirconium oxide, niobium oxide, lanthanum oxide, cerium oxide, tantalum oxide, aluminum oxide, yttrium aluminum oxide, aluminum nitride, and zirconium nitride. 0001
to 0.03 i parts to make a raw material powder,
The raw material powder is heated at 1650°C to 1°C in an atmosphere completely enriched with nitrogen.
It is characterized by heating to 500°C.

According to the present invention, silicon nitride for structural materials, which is fine-grained and of high quality and requires excellent mechanical strength, thermal shock resistance, and chemical stability at high temperatures, can be produced with high yield and at low cost. can.

Below, nine aspects of the present invention will be explained in more detail.

In the present invention, the mixing ratio of silicon dioxide and carbon is preferably 0.4 to 2-4 parts by weight per 1 part of silicon dioxide. This is because when the amount exceeds 0.4 parts by weight, the reactivity is certainly improved by the excess amount of carbon, but excess carbon beyond the required amount will eventually be burned and consumed in the atmosphere. .

This is because synthesis of silicon nitride (81 mN4) in the presence of an excessive amount of carbon increases manufacturing costs.

In addition, as an fA additive, lithium hydroxide (LioH)
.

Germanium oxide (oeo2), yttrium oxide (Y
2O, ), zirconium oxide (Zr02), niobium nide (NA20s), lanthanum oxide (Laa os ), cerium oxide (CeO2) + tantalum oxide (TIZ2 o
s), magnesium aluminum oxide (MgAl2
O4), yttrium aluminum oxide (Ys Al
s 012 ) + aluminum nitride (AIN),
One or more types of zirconium nitride (ZrN) are used.

The reason why these additives are effective in producing the excellent silicon nitride described above is that they are effective for producing silicon dioxide (sho) and carbon (C).
This is thought to be because it suppresses the production of by-products such as reverted silicon and fibers during total synthesis of silicon nitride from ) and acts effectively on sintering of silicon nitride powder. Here, the addition ratio of this additive is preferably 0.0001 to 0.03 parts by weight per part by weight of silicon dioxide. This is because if the additive is added in a proportion of 0.0001 mv/m, the production rate of silicon nitride is low and high quality silicon nitride cannot be obtained. In addition, if the amount exceeds 0.03 parts by weight, no improvement in by-product suppression effect can be expected even if all the additives are added, and addition of an excessive amount increases the particle size of silicon nitride. It is.

-! What is the gas used as the reducing/nitriding atmosphere?

Only nitrogen (N2) gas may be used, but hydrogen (N2) gas may also be added to the gas. In the latter case, it is possible to promote the nitriding reaction and further reduce the total particle size of silicon nitride (st, N4). Here, when hydrogen is included as the reducing/nitriding atmosphere, the mixing ratio of the gas mixture is preferably 30 volumes or less of hydrogen and the remainder essentially nitrogen. This is because if the mixing ratio of hydrogen exceeds 50 volumes, by-product silicon carbide (SXO) is produced, making it impossible to obtain high-quality silicon nitride.

Further, the heating temperature during reduction and nitriding is 1'350°C to 1500°C. This means that the heating temperature is 165
If the temperature is less than 0°C, unreacted silicon dioxide (5i
Offi) may remain.
In addition, if the temperature exceeds 1500°C, silicon carbide (S1
This is because C) is produced as a by-product, making it impossible to produce the desired high-quality silicon nitride with a good yield.

Note that when the silicon nitride powder produced by the method of the present invention is sintered, it becomes a sintered body having high high-temperature strength, high thermal sanitizing properties, high chemical stability, etc.

Example In this example, a raw material powder was prepared by mixing silicic anhydride as silicon dioxide, a carbon blank as carbon powder, and additives in the proportions shown in the table, and the raw material powder was used to manufacture the present invention. Silicon nitride was produced by this method, and the obtained silicon nitride was subjected to substance identification tests, scanning electron microscopy observations, and particle size measurements.

That is, first, silicic anhydride (5iC1a) and carbon black ((3) were mixed in the proportions shown in the table, and then mixed for 10 hours in a polyethylene container. Then, they were dried in a drying container. After volatilization, the solidified nodules were crushed in a mortar to obtain raw material powder.

Next, the obtained raw material powder was poured into a graphite boat (inner dimensions 10×1
After filling 22 ops into a 5×70 mm tube, it was loaded into a tubular siliconite furnace. Then, nitrogen gas and hydrogen gas are introduced into the tubular siliconite furnace at the mixing ratio shown in the atmosphere column of the table (
The graphite powder was maintained at the following heating temperature for 10 hours while flowing under standard conditions (converted to standard conditions), thereby completely reducing and nitriding the raw material powder to obtain a mixture of silicon nitride and carbon.

In the above, the raw material powder composition in the above table is shown in parts by weight added to 1 part by weight of S10. Also.

The heating temperatures for reduction and nitriding were sample numbers 1.4 to 7.
9 to 20 is 1450°C9 Sample number 2 is 1370°C1
Sample number 6 is 1400°C9 Sample number 8.21 is 150°C
It was 0°C.

Further, the mixture was transferred to a porcelain crucible and heated to a temperature of 650 in an air furnace.
The mixture was heated at °C for 5 hours to burn and remove residual hydrogen, thereby obtaining silicon nitride (sample numbers 1 to 21).

Regarding the shape of the silicon nitride obtained in the above manner, its surface was examined using a scanning electron microscope (SEM).
Observation was made using an electron m1 microscope (abbreviation for electron microscope). As a result, all of the silicon nitride obtained was granular, and no impurities such as fibers were found.

Further, as a representative example, a micrograph (magnification: 2800 times) of the surface shape of silicon nitride of sample number 4 is shown in FIG.

In addition, the particle size of the obtained silicon nitride was measured using a total light transmission type particle size analyzer. The results obtained from the particle size measurement are shown in the table.

Furthermore, all substance identification tests for silicon nitride obtained by X-ray diffraction using a Kobal) K extension were carried out.

Table 1 shows the results of the substance identification tests for sample numbers 1 to 21.

On the other hand, as a comparative example of this example, no additives were added to the raw material powder (sample number CI, 02), the heating time was (i7
Silicon nitride for comparison (sample numbers 01 and 02) was obtained by the same manufacturing method as the manufacturing method of the present invention described above except that the heating time was 5 hours (sample number C1). 8EM observation was performed in the same manner as above for silicon nitride manufactured by the comparative method. W4 imitation mirror pages (magnification: 2800 times) of the surface shapes of comparative silicon nitride of sample numbers C1 and C2 obtained in this way are shown in FIGS. 2 and 3, respectively. As a result, it can be seen that in the case of sample number C1, fibrous material was produced. Further, the particle size of the silicon nitride of the obtained sample number C2 was measured using a total light transmission type particle size analyzer. The results obtained from the particle size measurements are shown in the table.

Furthermore, a substance identification test was conducted on the comparative silicon nitrides obtained with sample numbers C1 and 02. The results of the substance identification test are shown in Table 9.

In the table, the raw material powder composition is shown in parts of M added to 1 part by weight of 5iO3. In addition, the heating temperature for reduction and nitriding is 1400°C for sample number C9.
2 was 1450°C.

As is clear from the table, the silicon nitride products produced by the method of the present invention (sample numbers 1 to 21) are fine silicon nitride particles in all cases, of which 90% of the α-type silicon nitride is
% or more.

It can be seen that all of the products are α-type silicon nitride.

On the other hand, in the case of sample number C1, it was a mixture of silicon nitride and silicon carbide.

As is clear from Figures 1 to 3.

The silicon nitride manufactured by the manufacturing method of the present invention (sample number 4, FIG. 1) is only fine-particle silicon nitride powder, but in the case of comparative example c1 (FIG. 2).

The formation of fibrous substances was observed, and in the case of Comparative Example a2 (FIG. 6), the particle size was large and non-uniform.

As described above, it can be seen that fine grained silicon nitride powder of good quality can be obtained by the manufacturing method of the present invention.

[Brief explanation of drawings]

The figure shows an example of the present invention, and FIG. 1 is a micrograph (magnification: 28
00x), Figures 2 and 3. Micrographs of the surface shapes of comparative silicon nitrides C1 and C2 obtained by the comparative method of this example (each at a magnification of 280
0 times). Patent applicant Toyota Central Research Institute Co., Ltd.

Claims (1)

[Claims] (1) 0.4 to 2 parts by weight of carbon powder per 1 part by weight of silicon dioxide, lithium hydroxide, germanium oxide, yttrium oxide, and zirconium oxide. Niobium oxide, lanthanum oxide, cerium oxide, tantalum oxide, aluminum oxide, aluminum oxide, aluminum yttrium, aluminum nitride. A raw material powder is prepared by mixing 0.0001 to 0.03 parts by weight of an additive consisting of two or more types of zirconium nitride per implantation, and the raw material powder is heated to 135% by weight in an atmosphere containing nitrogen.
A method for producing silicon nitride, which is characterized by heating to 0'C to 1500'C. . (3) The atmosphere consists of less than 30% hydrogen by volume and the remainder