JPS6287408A - Manufacture of silica having specific particle shape - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for producing silicon having a specific grain shape.

BACKGROUND OF THE INVENTION High performance ramic (RJ) materials are of great interest in a number of applications due to their unique properties.

The materials mentioned may consist, for example, of oxides, carbides or nitrides of the elements aluminum, silicon or zirconium, or of aluminum titanate or biset titanium. The production of the actual workpiece is mostly carried out by powder metallurgy, for which very fine powders of the abrasive materials are used.

In addition, due to the high solid state potential at high temperatures, silicon carbide (
In addition to silicon nitride (SiC), silicon nitride (Si3N4) is particularly important. SIC powder is usually obtained by grinding conventionally produced silicon carbide (which is extremely expensive due to the hardness of the material), but various methods for producing silicon nitride powder have been proposed. It's because of that. There have been many attempts to produce Si3N4 by repeated nitriding and grinding of silicon. Other options are the reaction of silicon dioxide with carbon and nitrogen or the reaction of silicon tetrachloride with ammonia, with the intermediate formation of siliconamides or siliconimides.

Common to these methods is the disadvantage that the resulting powder is contaminated. Impurities originate from the grinding process or are brought about by intermediates or by-products that cannot be completely separated (e.g. chlorine-containing compounds) or by contact with moisture or air oxygen, often even in the course of a multi-step operation. It's almost impossible to avoid.

Impurity fractionation is a drawback insofar as the high temperature resistance of the ceramic material is adversely affected by the impurities themselves or by the use of large amounts of sintering aids (for example Y2O3 in the case of silicon nitride) accompanying the impurities.

References CW, R., Cannon et al., J.A.
m.

Ceram, Soc, 65+7 (1982L 3
Pages 24 to 635] describes a method that does not cause the above-mentioned difficulties. According to this, fine silicon or silicon nitride powder is 5IH4 or 5iH474JH3
It is prepared from a mixture by heating with Radiation light under reduced pressure. Apart from the risks associated with the use of large silanes, implementation on an industrial scale is hardly foreseeable due to the extremely high energy consumption.

Problem to be Solved by the Invention The invention therefore develops an industrially viable method for producing ultrafine powders from silicon, silicon carbide or silicon nitride as pure as possible, which does not have the drawbacks mentioned above. It is based on the challenge of

Means for solving the problem This problem is solved according to the invention by the following steps: Firstly, the BET surface area of the reed is 0.5 m”/j! ~100 μm) elemental silicon at a temperature above 1100°C, preferably 12000°C.
React with excess silicon tetrachloride at a temperature above 0. This will form gaseous silicon dichloride (S i Cl2). The gas mixture resulting from 5iCt4, consisting of 51ct2 and excess SICA4, is then 6D
Cool to the temperature of O'O.

SI C12 is disproportionated to EliC4 and Sl in the reverse reaction of the production reaction. This anti-r'r: (rf, , literature [Harald Schaefer (Harald 5chaefer)
), “Chemische Transvoltaicionen (Chemische Transportr
eaktionen)'', Verlag Chennie.

1962, p42-44] K is described in principle as a transport reaction to form long, fully grown needle-like crystals of elemental silicon. There are contradictory temperature descriptions here.

General reaction Si +SiX4≠2SiX2 (X=-FX
CL, Br, ■), 110[1→90
Although a temperature drop of 0'C is described, the reaction S i +Si C64#2 EliCt is particularly relevant to the present invention.
In case 2, a temperature drop of 1300→1100° C. is described. According to Schaefer in the above-mentioned document, in the case of very large temperature drops, a significant portion of 5icz2 produced in the hot zone in an open flow device enters the cold zone without disproportionation9, where it combines with 5iCt4. to form a polychloride of the formula 5inC721+2. However, surprisingly, Si +5icz4. ==:25
The reaction of IC12 can also be used for the production of fine silicon (particle size: 1 μm).

In detail, the present invention involves reacting silicon and gaseous carbon tetrachloride at high temperatures to form silicon dichloride, and disproportionating this at low temperatures to produce silicon and tetrachloride having a specific grain shape. In a method for producing silicon with a specific grain shape by producing silicon, granular or flake silicon is used to produce fine silicon with a grain size of 1 μm and a BET surface area >101712/g. , 1100℃
react with excess silicon tetrachloride at a temperature in excess of
The method is characterized in that the silicon dichloride produced is disproportionated by cooling from this temperature without a stopping point while maintaining a residence time of 5 to 100 seconds to produce the desired fine silicon and silicon tetrachloride. . Here the residence time is 20°C and l
is the time relative to the volume of the gaseous reaction mixture, calculated in terms of bar.

Furthermore, the process according to the invention can advantageously be carried out selectively in the following manner: a) silicon in powder form or in the form of 1-I' strips of 1200 to 14
React with excess silicon tetrachloride at a temperature of 00°C.

b) 900 with a residence time of 10-60 seconds during cooling
A temperature range of ~600'C is passed.

C) The reaction is carried out in a heated fluidized zone arranged vertically and charged with silicon powder or flakes, with excess silicon tetrachloride introduced from below.

d) Cooling of the reaction mixture is carried out in the presence of nitrogen.

The fine silicon produced according to the present invention is silicon nitride (si
3N4) and silicon carbide (SiC) [Preparation (Q) and Properties of Elol] -1d
5tate Materials), ■o1.7,
Growth Mechanism
ismsand Si'1icon N1tride
) (edited by W. R. Wilcox,
Marcel De'kker
Society, New York 1982), especially pp. 161 et seq. and W. R. Cannon et al., supra].

The FiA of the present invention also relates to a method for producing a fine silicon compound characterized by using the fine silicon obtained according to the present invention. That is, fine silicon nitride is produced by reacting the obtained fine silicon with nitrogen at a temperature of 1300 to 1500° C. by a method known per se. Similarly, finely divided silicon carbide is produced by reacting the obtained finely divided silicon with hydrocarbons at high temperatures in a manner known per se.

The 5iC64 produced during the reverse reaction can be returned to the stage of 5icz2 production, thus providing a kind of circular method for producing fine silicon from coarse particles. However, the reverse reaction can also proceed in the presence of nitrogen, so that the fine silicon particles are coated with a nitride film and are thereby protected from the action of oxygen.

The finely formed silicon can be reacted with known methods in the same apparatus to silicon nitride, for example with nitrogen, or with gaseous hydrocarbon compounds such as methane, ethylene, etc., or to silicon carbide. The reactions are carried out in separate steps.

In either case, a high degree of fineness of silicon particles can be obtained.

Examples Example 1 40 g of silicon powder was heated to 1230 °C in a tube furnace in a vertically arranged quartz tube (45 mm inner diameter, 80% length) with a fused frit (particle distribution = 60-10
0μm22%, 30-60μm22%s <30μm5
6%; BET surface area < 0.1 m2/j; l). In a round-bottomed flask, 5iCt4 is boiled (57° C.) and passed from below into a quartz tube in a flow of argon (20 l/h) for 5.5 hours, maintaining an evaporation rate of 5.29/min. At the top of the deposited silicon powder, °τ spans a section of 35 CrrL.
The humidity temperature drops from 121,000 to 600°C, and inside the deposited silicon powder the temperature decreases to 900°C over a section of 20 (1n).
The temperature drops from 600°C to 600°C. 21g of the same silicon powder in the reaction is 5
Reacted with iC44. At temperatures above 900°C no solids were deposited, but in the 900-600°C zone a dense layer of elemental silicon was coated. The residence time in this zone was 18 seconds. In addition to this dense silicon,
The desired fine silicon powder (average particle size 0.1 μm; BFiT surface Jjf 22 m
2Aj) 11.0g was deposited. Next, add this powder to 14
Reacted with nitrogen at 00°C. The resulting product is X#J'T
According to Kanho, it is mainly composed of E113N4 and has a BET surface of 1't19m''/,9.

Example 2 Example 1 was repeated with the following difference: Reaction of silicon powder f11 was carried out at 80°C. Into a round bottom flask with an internal temperature of 100°C, 51 ct of 411/mIH was added dropwise using a biurette. The vapors of s,tct4 generated in this case were passed through the quartz tube for 3.5 hours in a stream of N2 (50//h). At that time silicon 21.5! j was reacted. The length of the temperature zone from 900 to 600℃ is 14crr
It was L. Dense silicon deposition occurred in this zone.

Residence time in this zone was 10 seconds. 7.0 g of the desired finely divided silicon were isolated from the cooler quartz tube section that followed above. The silicon had an average particle size of 0.1 μm and a BET surface area of 26″27g.

Example 3 Example 1 was repeated, but the following differences were made 2 5 iCt in a round bottom flask heated to 100°C.

0.5,! i'/min 51 cz, fed for 6 hours by means of a pulette and then evaporated immediately,
The flow was conducted through the quartz tube by means of an albo-//h flow (10//h). At this time, 9 g of silicon was reacted. 900 of quartz tube
The ~600°C temperature zone was 22 degrees long. A relatively large amount of dense silicon was deposited in this zone. Residence time taq in this zone.

It was seconds. 1 g of the desired fine silicon powder was obtained from the lower temperature quartz tube section continuing above. The average particle size of the powder is 0.6μ
m and BET surface fjf12rrL2/,9.

Example 4 (comparative example) Example 1 was repeated but with the following differences: 25iC43'/
/ min was added dropwise during 3.5 h into a round-bottomed flask heated to 100 °C by billet, and then the instantly evaporated 5icz4 was passed through a quartz tube by a flow of N2 (240//h). Ta. At this time, silicon 22. V was reacted. Furthermore, the cross section of the tube above the frit is a protective tube made of aluminum oxide ceramic (inner diameter '50 mm).
narrowed by the use of Only a very small amount of elemental silicon was deposited in the 900-600°C temperature zone of the quartz tube. Instead, a less volatile polysilicon chloride was found in the lower temperature section of the reaction tube. The residence time in the 900-600°C temperature zone with a length of 25 cm was 2 seconds.

Average particle size 0.1 μm and BET surface N25m2/E
A total of only 1 g of silicon powder having .

Claims (1)

[Claims] 1. Silicon is reacted with gaseous silicon tetrachloride at high temperature to produce silicon dichloride, and this is disproportionated at low temperature to produce silicon and silicon tetrachloride having a specific grain shape. In order to produce silicon having a specific particle shape by producing fine silicon having a particle size <1 μm and a BET surface area >10 m^2/g, powdered or flaky silicon is Reacting with excess silicon tetrachloride at a temperature above 1100°C, the gaseous reaction mixture is cooled as quickly as possible to 900°C and from this temperature without a stop point, maintaining a residence time of 5 to 100 seconds. 1. A method for producing silicon having a specific grain shape, which comprises cooling to 600° C. and disproportionating the resulting silicon dichloride to produce desired fine silicon and silicon tetrachloride. 2. The method according to claim 1, wherein silicon powder or flakes are reacted with excess silicon tetrachloride at a temperature of 1200 to 1400°C. 3. 900°C while maintaining a residence time of 10-30 seconds during cooling.
Claim 1 in which a temperature range of ~600°C is passed.
or the method described in paragraph 2. 4. Claims 1 to 3 in which the reaction is carried out in a heated fluidized zone arranged vertically and charged with silicon powder or flakes, and excess silicon tetrachloride is introduced from below. The method described in any one of the above. 5. The method according to any one of claims 1 to 4, wherein the reaction mixture is cooled in the presence of nitrogen. 6. A method according to any one of claims 1 to 5 for producing fine silicon used for the per se known production of silicon nitride. 7. A method according to any one of claims 1 to 5 for producing fine silicon used for the per se known production of silicon carbide. 8. Particle size <1 μm and BET surface area >10 m^2/g
In order to produce finely divided silicon with
and from this temperature to 600° C. with a residence time of 5 to 100 seconds without a stop point to disproportionate the resulting silicon dichloride to form the desired fine silicon and silicon tetrachloride. 1. A method for producing a fine silicon compound from silicon, the method comprising using fine silicon obtained by producing a silicon compound. 9. The fine silicon is reduced to 3000 to 150 by a method known per se.
9. The method according to claim 8, wherein fine silicon nitride is produced by reacting with nitrogen at a temperature of 0°C. 10. The method according to claim 8, wherein fine silicon carbide is produced by reacting the fine silicon with a hydrocarbon at high temperature by a method known per se.