JPS5997506A - Manufacture of silicon nitride - Google Patents

Abstract

PURPOSE:To manufacture efficiently silicon nitride of high purity and quality at a low cost by heating a mixture of carbon with diatomaceous earth at a specified temp. in a nitrogen atmosphere. CONSTITUTION:Carbon powder is mixed with powder of diatomaceous earth in (0.4-4):1 ratio to prepare a powdered mixture. Carbon black, pitch, graphite or the like is used as the carbon. The powdered mixture is heated in a nitrogen atmosphere to convert SiO2 in the powder into silicon nitride by reduction and nitriding. The reduction and nitriding temp. is 1,350-1,500 deg.C, and the heating time is 5-10hr.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for manufacturing silicon nitride.

Silicon nitride (SiaN4) has been actively developed for various uses because its sintered body has excellent mechanical strength, thermal shock resistance and chemical stability at high temperatures, and the manufacturing of silicon nitride itself has been actively conducted. Methods (intensive studies are being conducted to obtain silicon nitride of high purity and good quality even if it is hard).

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

One example of these manufacturing methods is:

(1) Method of nitriding metal silicon powder.

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

(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 conventional techniques, in method (1), the price of the metal silicon powder is extremely high, so the manufacturing cost of the final product, silicon nitride, is also very high. This is a difficult IF. Method (2) can obtain silicon nitride at a relatively high yield, but has the drawbacks of poor mass productivity, high raw material costs, and high production costs. On the other hand, method (8) uses silicon dioxide, which is abundant in resources, 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 (8), silicon dioxide (Si(h
) as a starting material.

This method involves mixing silicon dioxide (Sins) and carbon (C) in a range of 1800 to 150% in a nitrogen atmosphere.
Silicon nitride (Si3Na) is obtained by heating to a temperature of 0°C. Silicon dioxide and carbon as raw materials used here are preferably rich in 1-reactive V, and a typical example of silicon dioxide is:

Amorphous silica with a large specific surface area (white carbon, etc.)
etc. are used.

When the amorphous raw material of Kori et al. is used.

When synthesizing silicon nitride, the stoichiometric ratio (K-(C)/(
Unless an excess of carbon (Kn 20) is added which is much larger than S 1O2) (mol)-〇, the rate of conversion of silicon dioxide to silicon nitride will be extremely low.

In addition, if excess carbon is added, this excess carbon will eventually be burned and consumed in the atmosphere, so synthesis of silicon nitride (Si3N4) in the presence of excess carbon will result in high production costs. Industrially disadvantageous.

Therefore, in view of the conventional problems 1 as mentioned above, the inventors of the present invention have conducted various studies to solve the problems and have completed the present invention. (Objective of the Invention) The purpose is to provide a method for efficiently (and inexpensively) manufacturing high-purity, high-quality silicon nitride.

(Structure and Effects of the Invention) The present invention provides a method for producing silicon nitride, which is characterized by heating a mixed powder of carbon (C) and diatomaceous earth (SiO□) at a temperature of 1350 to 1500°C in a nitrogen atmosphere. It is.

By the manufacturing method of the present invention, high purity and high quality silicon nitride can be manufactured easily and at low cost.

The following two inventions will be explained in more detail.

The mixed powder used in the present invention is obtained by mixing carbon (C) and diatomaceous earth. Carbon (C) as a raw material
can be either crystalline or amorphous, and is a typical example.

Carbon black, pitch, graphite, etc. The carbon may be any substance that is essentially composed of carbon (C)t.

Furthermore, diatomaceous earth is an aggregate of fossilized diatoms of cryptoflowering plants, and its main component is silicon dioxide (Si(h)).The diatomaceous earth has micropores and is capable of adsorbing liquids.

It has the characteristics of having activities such as absorption performance. In the invention, the diatomaceous earth may be left in its produced state.

Diatomaceous earth purified by chemical treatment or the like may also be used.

Next, the above carbon and diatomaceous earth are mixed. Is the mixing done by wet mixing in a mixing container? Go ahead.

Obtain a mixed powder. In this case, the mixing ratio of carbon and diatomaceous earth is preferably 04 to 4 carbon to diatom ±(Si(h)1) in raw material composition ratio. This is because if the raw material composition ratio is less than α4 carbon to diatom ± (SiOz), silicon dioxide will remain as an unreacted substance in the ninth reduction/nitridation step.

In addition, if the carbon content exceeds 4, no significant effect will be seen even if additional base guests are added, and on the contrary, using too much carbon will increase manufacturing costs, which is very disadvantageous industrially. be.

By reducing and nitriding 1, silicon nitride is obtained.

Here, the reduction/nitriding temperature is +! , 1350℃ or higher 150
The heating time is 5 to 10 hours at a temperature below 0°C. This is because if the heating temperature is lower than 1850° C., there is a risk that unreacted silicon dioxide may remain. Further, if the temperature exceeds 1500°C, silicon carbide (SiC) is likely to be generated.

Here, the silicon nitride obtained by the method for producing silicon nitride of the present invention is a high-purity and high-quality silicon nitride, but it can be made even more pure and high-quality by further heat treatment to remove residual carbon. It can be silicon nitride. This heat treatment is preferably carried out in the atmosphere at a temperature in the range of 500 to 700°C for 5 to 10 hours.

Furthermore, diatomaceous earth is used as the silicon dioxide (Sin2) material in the present invention because it is an abundant resource, and the raw material can be obtained at low cost.
oz ) KtU K It is extremely effective in promoting the production reaction during the production of silicon nitride (Si3Nt) for comparison, and in the synthesis of silicon nitride (Si3N4), carbon (C) has a stoichiometric ratio (K= This is because the same amount of carbon as in 2) is sufficient. Although it is not fully clear that diatomaceous earth promotes the production reaction during the production of silicon nitride, the activity of the micropores of diatomaceous earth increases the conversion from silicon dioxide (Sin2) to silicon nitride (sj3N4). It is thought that this has an effective effect on the reaction.

By the manufacturing method P of the present invention having the above configuration, high purity and high quality silicon nitride can be manufactured easily and at low cost.

Furthermore, the silicon nitride obtained according to the present invention has high purity and good quality, so when it is made into a sintered crystal, it has excellent high temperature strength and high thermal shock resistance.

In addition, diatomaceous earth as a raw material for silicon dioxide used in the present invention is an abundant resource and can be obtained at low cost.
Since high-purity silicon nitride can be manufactured at low cost and can be mass-produced, the present invention is an industrial method for manufacturing P-superior silicon nitride. show.

In this example, a mixed powder was prepared using a car pump hook as Bg and diatomaceous earth as raw materials, and then the mixed powder was reduced and nitrided to produce silicon nitride, and the substance identification of the obtained silicon nitride was performed. I conducted a test.

The manufacturing method in this embodiment is as follows.

That is, first, a powder having a purity of 95% and a specific surface area of 6 m 2 /g was prepared. Next, the raw material powder and ethanol as a dispersion medium were placed in a polyethylene container and mixed for 15 hours on a ball mill stand. Next, the above mixture was dried in a drying container at a temperature of 60° C. for 20 hours to volatilize the solvent, and then the solidified mixture was ground in a mortar to obtain a mixed powder.

After that, add 20g of each mixed powder to the inner size of 10 x 15 x 7.
After filling the 0 m graphite port, it was loaded into the tubular series-7) furnace. Then, the nitrogen gas was pumped into the tubular silicone furnace at 2.5 m/min. The graphite port was heated to the temperature shown in the table (1350 to 1500°C) for about 1.5 hours while flowing at a rate of OI (converted to standard conditions), and then Alternatively, a mixture of silicon nitride and carbon was obtained by heating the mixture for 10 hours.

Further, the mixture was transferred to a porcelain crucible and heated to a temperature of 650°C in the atmosphere.
A heat treatment was carried out at 50° C. for 5 hours to burn and remove residual carbon, thereby obtaining grayish brown silicon nitride (sample numbers 1 to 7). Here, for comparison.

A white-brown comparative silicon nitride (sample number CI) was obtained in the same manner as above except that the heating temperature during reduction and nitridation was 1300°C.

Silicon nitride obtained as above (sample number 1~?,
A substance identification test for CI) was carried out by powder X-ray diffraction using cobalt Ka rays. The composition ratio of silicon dioxide (SiO2) and carbon (C) obtained by the X-ray diffraction and σ
The X-ray diffraction intensity of -8i3Na (102 plane) is shown in Figure t and curve 1, and the substance identification results are shown in the table together with the color tone of the product. In addition, the numbers in parentheses indicate the production rate of the product (
weight%).

The inequality symbol rA))BJ has a generation rate of 80.
Indicates that it is more than % by weight.

On the other hand, for comparison with Examples, the silicic acid released by hydrolysis with 79m acid (12N) was washed with water in a commercially available water glass (No. 8).
The amorphous silica (white carbon; specific surface area: 51077X'/g) obtained by drying and the above carbon black as a carbon material were further heated to remove residual carbon and compared with the gray or white-gray color. Silicon nitride for use was obtained.

Silicon nitride for comparison (silicon nitride for comparison 02 to C5
) was subjected to powder X-ray diffraction in the same manner as above. The X
The relationship between the composition ratio of silicon dioxide (SiO2) and carbon (C) obtained from line diffraction 1 and the X-ray diffraction intensity of α-8isNi (102 plane) is shown in curve 2, and the material identification results are also generated. Each is shown in the table along with the color tone of the object.

/ As is clear from the table, reduction and nitriding were carried out at a temperature of 1350 to 150 using the method of the present invention using diatomaceous earth as a raw material for silicon dioxide.
When carried out at 0°C (sample numbers 1 to 7), no unreacted silicon dioxide (Si02) remains, and nitridation has progressed sufficiently to produce only silicon nitride (S is N, a ). I understand. However, the same method [when the heating temperature during reduction and nitriding was 1800°C (sample number CI)
It can be seen that m-conversion is somewhat insufficient, and a slight amount of silicon oxynitride (Si2N20) is generated in addition to silicon nitride (Si3Nt).

On the other hand, when amorphous silica was used as the silicon dioxide raw material (Comparative Examples IC2 to C3), nitridation did not proceed much and it was found that a large amount of unreacted silicon dioxide was present.

Also, as is clear from Figure 2, K((C) and (Si02)
The relationship between the diffraction intensity (102 plane) of α-type silicon nitride (a-S 1iNa ) is It can be seen that the amount of α-type silicon nitride produced is 2 to 4 times higher than when amorphous silica is used as the silicon dioxide raw material.In addition, when amorphous silica is used as the silicon dioxide raw material, In this case, if the amount of carbon decreases by 1 F, the amount of silicon nitride produced decreases.

It can be seen that when diatomaceous earth is used, on the contrary, the amount of silicon nitride produced tends to increase.

[Brief explanation of drawings]

The figure shows an example of the present invention, and is a diagram showing the relationship between the raw material composition of silicon nitride obtained in the example and the X-ray diffraction intensity of α-type silicon nitride. Patent applicant Toyota Central Research Institute Co., Ltd.

Claims (1)

[Claims] (A mixed powder of 11 carbon and diatomaceous earth is
A method for producing silicon nitride, the method comprising heating at a temperature of 850 to 1500°C. (2) The method for producing silicon nitride according to claim 1, wherein the mixing ratio of carbon and diatomaceous earth is α4 to 4 carbon to ±1 diatom in raw material composition ratio.