JPS5891014A - Continuous manufacture of silicon nitride - Google Patents

Abstract

PURPOSE:To obtain silicon nitride continuously and easily by heating pellets contg. silica, fine carbon powder and chaff powder in a prescribed ratio in an atmosphere of gaseous N2 or NH3 to cause reduction and nitriding. CONSTITUTION:A mixture consisting of silica and fine carbon powder in <=4 molar ratio of C/SiO2 is prepared. To the mixture is added 5-50% as dry matter of chaff powder, and they are pelletized. The pellets are fed to a vertical electric furnace, and after introducing gaseous N2 or NH3, the pellets are heated to cause reduction and nitriding reactions. Thus, silicon nitride is obtd. continuously and easily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing silicon nitride by sequentially blowing silica and carbon threads.

Silicon nitride has excellent sieve strength, high heat resistance, thermal shock resistance, and corrosion resistance, and is one of the heat-resistant paulownia materials that is considered promising along with sialon and silicon carbide.

In general, the manufacturing methods for silicon nitride include: ■Nitriding silicon, ■Silicon trichloride, silicon trichloride, and ammonia.
．． Methods of reaction with a gas such as N 2 +ii 2 and (2) nitriding of a silica and carbon mixture are known. However, method (2) has drawbacks such as the raw material silicon being extremely planar, and the nitriding reaction being an exothermic reaction that tends to be extremely unstable. In method (2), the raw materials have a crystal value and the reaction rate is still low.
In addition, HCt is generated as a by-product, which poses problems in terms of corrosion resistance of the equipment and environmental pollution during operation. In the method (2), raw materials with bacterial purity are available at relatively low cost, but as there is no continuous method for continuous production of the bacteria, the result is a method for producing sieves.

Taking into consideration the state situation mentioned above, the present inventor has conducted extensive research into a method for producing silicon nitride continuously and inexpensively on an industrial scale, and has now developed the present invention.

The method of the present invention will be described below. In this method, the raw materials, silica from Azeishigin and carbon such as coke, have good reactivity and are easy to granulate, so the upper limit of particle size is 20μ or less (μF). (0), Hiroq
It is desirable to set the value to μF. Is it better to consider only the anti-16 nature of this degree?1. /
When it becomes μF, the granulation properties are very poor, and on the other hand, the VC pellets are damaged and cause the gas to become 17f', oxidized, anti-oxidized, and sexualized. In addition, for reaction 1 only, we compared the case where silica, 20μF1 coke 4tμμI− were used as raw materials, and the case where both silica and coke were used as raw materials, but the reaction rate of both was compared. 3
There is not much difference in the lower divisions, and in the end, the former division has an advantage due to the cheapness of driving. Therefore, S i 02 /~, 20μ, C no~
It is preferable that g≠μ.

The mixing molar ratio of silica and carbon is 2.5≦C/
The range of S i Q 2≦g was good, and the theoretical mixture of C/5i02 = 2, which was rich in cicabon, yielded a better result. The reason is that Sj Q 7. generated during the reaction process. This is because r carbon is collected and raw material clogging due to SiO precipitation is suppressed, and at the same time, the IV element in the inverse ratio system is released as CO to the outside of the yarn, and the generation of silicon ogishinirite and the like is also suppressed. In addition, the amount of carbon is C/Si 02
) If p is the heating and cooling of unreacted carbon, the electric power intensity will be V.Furthermore, the most important imitation of the present invention is to dry the mixture of silica and carbon with rice husks. (outside b11
9) j-50% addition. Paddy 0.1%,
N2 0.7%, Ca: trX
Mg: tr.

Mn:tr etc., and when caulked, 5iQ2:Ar
4.C:3! %. Therefore, the mole settlement C/S
i Q 2-. 2.7, and can be used as a raw material for reduction nitriding. However, when rice husks are used alone, the bulk specific gravity of the filling is small, so the energy density per raw material unit mold is too high, which is contrary to energy conservation.In addition, when cutting out products, the raw materials and products fall under their own weight, so the specific gravity of the rice husk is low. If there is no loose material, even the slightest obstruction can easily cause raw material clogging.

The rice husk is preferably 71LtpF in order to have good granulation properties, uniform dispersion, and a good reaction rate.

If rice husk is added to the silica and carbon mixture and pre-granulated, the filling ratio of the granulated pellet will be small and the strength of the granulated pellet will be weak.If the added violet is less than J, the organic matter in the rice husk will be reduced. CM with small pores generated when fc is decomposed and light is generated.
This makes it difficult for the N2 material to diffuse into the inside of the pellet. The size of this pellet is suitably in the range of 6 to 20 rran.

When pellets containing j-10% of rice husks are fed from the upper part of the vertical furnace, the rice husks in the pellets are caulked in the preheating region of ≠00 to g00°C to become porous pellets.

Further, when the pellets reach the reaction region, first, a nitriding reaction occurs with the X4 elements of the rice husks subjected to coking δ, producing α-type desired silicon. Next, 1. Reduction of the silica and carbon mixture;
A nitriding reaction begins to produce α-type silicon nitride. The reason why α-type silicon nitride is produced in the above reaction is not clear, but it is thought that the nitrogen produced in the rice husks makes the surrounding environment more likely to produce α-type silicon nitride.

The reduction and nitriding reactions are carried out at /3jθ~/330°C, preferably /310~/1110°C, by flowing N2 or NH3h, or a mixture thereof, for a period of 7 to 5 hours. Appropriate.

Next, examples will be shown to explain the method of the present invention.

FIG. 1 shows an example of a vertical furnace for carrying out the method of the present invention.

[Example-)]

Grind silica stone (Si02 Tata, Ri%) with a ball mill /j
μF1 average particle size was defined as zμ. Similarly, the 19F1 average particle size of the coal coke was set to 7θμ.

The above raw materials are blended at a molar ratio C/S of 102=3,
Add t9 shell of geμF to the blended product in a dry state.
% was added and mixed with a blender.

This mixture was granulated using a pan pelletizer using polyvinyl alcohol as a binder to form pellets of size φ.

After drying the pellets at 100°C, the pellets are covered with 30 carbon grains of 7 mm Φ, and then re-fed into the vertical furnace 1, which can be closed, through the raw material inlet 2 at the top of the furnace, while being lowered by its own weight. The reaction was carried out using Hirono C. The residence time in the preheating region and the reaction region of the Jerome pellet was set to 100 m, respectively.
It is heated by heat exchange with the air. This heated N2 residue is used for the nitriding reaction in the reaction region 4, and the excess N2
G: Well, it rose with the CO generated by the reaction, and the temperature was lowered by exchanging heat with the raw material pellets, so gas emissions 1" 2
More discharge type. The produced silicon nitride-1 is taken out by the table feeder 5 of the lower furnace jη11 and stored in the raw material stock tank (sealable) 6. External charcoal coexists with the upstream self-produced silicon, but this can be separated by sieving.

In the figure, 7 is a raw material tank, 8 is a heat insulating layer, 9 is a graphite reaction wall, 10 is a storage keeper heater, and 11 is a bus bar.

The raw Knt force is s, oSi aN4-Kg/Hrs The product exhibits a grayish-black color, and becomes grayish-white after being treated in air at 100°C. The mold was molded on silicon nitride with O dust.

[Example-2] Four people poured N H3 gas into gas JW outlet 2, and
Silicon nitride was produced in the same manner as in Example 1, except that the lower blade of reactor 9 was cooled in parallel with the pellet, and the temperature of the product and exhaust gas was lowered and extracted. . The result is ≠Si 3 N 4 K g / 1-[r
α-type silicon nitride was obtained at a production capacity comparable to that of Example 1.

[Brief explanation of drawings]

FIG. 7 is a longitudinal sectional view showing an example of a vertical furnace for carrying out the method of the invention. 1... Vertical furnace, 2... Raw material inlet (gas outlet), 3... N24 population, 4...
・Reaction area, 5...Table feeder, 6...
... Live bacteria stock tank, 7 ... YA family tank, 8 ... Heat insulation layer, 9 ... Graphite reaction wall (7 sides 500 m), 10 ... ...Holder 11 Prisoner Blind Heater (Protection Pause 3Crnψ), 11...Busbar. Applicant: Akioro'Aneko Co., Ltd., )1

Claims (1)

[Claims] Molar ratio of silica and carbon fine powder, j≦C/5iQ
2≦g, and granulated this mixture by adding 5-SO in a rice husk powder dry calculation.The granulated pellets were passed through the upper part of a vertical electric furnace and heated with N2 , or a continuous method for producing silicon nitride, in which NH3 gas is exclusively introduced into the upper or lower part of the above f, heated and reduced, and the nitrided product is converted into mold.