JPS60255615A - Production of silicon - Google Patents

Abstract

PURPOSE:To produce highly pure Si, economically and efficiently, with a simplified means, by carrying out the complete reduction of a powdery mixture of SiO2 and a specific reducing agent instantaneously in a plasma gas stream. CONSTITUTION:1mol of powderly SiO2 (e.g. high purity quartz sand) crushed to about 200-325 mesh is added to a hot aqueous solution containing >=2mol of a reducing agent such as saccharose (in terms of C), kneaded homogeneously, dried, and pulverized to obtain powderly mixture of SiO2 and the reducing agent. The powder is thrown into the hopper 1, tansferred by H2 gas supplied to the feeder 2 attached to the bottom of the hopper 1, and introduced into the plasma torch 4 at the top of the reaction furnance 3. The powder is passed through the H2 gas plasma stream A of >=2,000 deg.C generated by the plasma torch 4, and is reduced completely and almost instantaneously to Si. The produced Si is cooled together with the gas stream with the cooler 5, separated from CO, H2 and stream by the separator 6, and delivered from the bottom of the separator 6.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing silicon, and more particularly, to a method for producing silicon by efficiently and economically reducing silicon dioxide using simplified means. .

Silicon is widely used in semiconductors used in transistors, ICs, etc., and also in solar cells and the like.

This type of silicon (St) is generally silicon dioxide (Si
It is produced by reducing O2).

The present invention reduces silicon dioxide to produce silicon, and by making the reduction method simple, efficient, and economical, it can be used as it is without further purification, for example, to produce silicon of the solar cell grade. The present invention provides a method for producing silicon of relatively high purity.

<Prior art and its problems> Conventionally, the following methods have been proposed for producing silicon by reducing silicon dioxide.

1) Reduce silicon dioxide to crude silicon, then reduce chloride (
For example, there is a method (Siemens method) in which silicon is produced by converting it into a form (trichloride) and then reducing it with hydrogen. This method is
Currently, this is the mainstream method for producing silicon for semiconductors, but while it can produce ultra-high purity silicon,
The problem is that the methods are complicated and the silicon obtained is extremely expensive.

11) Therefore, in recent years, a method using a high-temperature furnace such as an electric furnace or an arc furnace has been attracting attention again. Silicon dioxide and activated carbon or carbon blank as a reducing agent are loaded into the high-temperature furnace and a reduction reaction is carried out to reduce silicon. A manufacturing method has been proposed (Japanese Patent Laid-Open No. 136116/1983). However, according to this method, the intermediate product silicon monoxide (SiO)
There is a problem in that silicon carbide (8iC) and silicon carbide (8iC) result in a poor yield of silicon.

111) On the other hand, silicon dioxide powder is reduced by passing silicon dioxide powder through a reducing plasma gas flow, and at this time passing carbon powder as a reducing agent through g1. Method for manufacturing (JP-A-56-1691
No. 18), a method has also been proposed in which silicon dioxide powder is passed through a plasma gas stream and then introduced into a reaction chamber loaded with a reducing agent to reduce silicon dioxide and produce silicon. (Unexamined Japanese Patent Publication No. 58-69713)
. However, these methods have the problem that silicon dioxide is actually hardly reduced to silicon, or the yield of silicon is still poor.

<Problems to be Solved by the Invention> The present invention solves the problems in the conventional methods as described above in producing silicon by reducing silicon dioxide.The problems can be summarized as follows. That's right.

1) Problem that the method is complicated 2) Coupled with 1) above, the problem that the obtained silicon is extremely expensive and therefore uneconomical 3) The yield of silicon is poor However, in general, the present invention is based on the following formula, and when manufacturing silicon by reducing silicon dioxide, silicon dioxide is reduced. The present invention relates to a method for producing silicon characterized by passing a powder in which silicon and a reducing agent coexist in a plasma.

SiO2+ 2C-+Si + 2CO↑In the present invention,
As silicon dioxide, for example, quartz sand of relatively high purity can be used. Further, as the reducing agent, carbonaceous materials such as activated carbon and carbon black can be used, but it is preferable to use one or more types selected from hydrocarbon compounds or compounds containing oxygen atoms. .

Such reducing agents include paraffin, cellulose,
Various compounds can be mentioned, such as starch, phenol, and polyvinyl alcohol. In practice, the reducing agents listed above are used in the form of solutions, aqueous solutions, or dispersions thereof as a preliminary step to coexist integrally with silicon dioxide, as will be described later. soccer b-
It is even more preferable to use it in combination.

In the present invention, a powder in which silicon dioxide and a reducing agent coexist integrally refers to a powder in which the reducing agent is attached to the silicon dioxide powder, a powder in which the reducing agent is coated, and a powder in which the reducing agent is adsorbed. This refers to the form in which the silicon dioxide powder and the reducing agent are at least slightly joined together, and the two are physically separate and separate. It's not something that exists. Furthermore, in the present invention, passing the powder through plasma means placing the powder on a gas flow such as hydrogen gas or argon gas, and generating plasma using various plasma torches or arc generating electrodes. It is to let it pass inside.

FIG. 1 illustrates a system diagram of main parts in the present invention. First, a powder in which silicon dioxide and a reducing agent coexist is prepared, for example, as follows.

That is, in a heated aqueous solution of sucrose, 200 to 32
Add silicon dioxide powder pulverized to about 5 mesh and knead it uniformly. Thereafter, the mass was dried overnight at 150°C and then pulverized and classified. The powder to be present preferably has a particle size of about 200 to 325 mesh, and is preferably one in which a reducing agent is integrally co-existed so that the amount of carbon atoms is around 2 moles or more per 1 mole of silicon dioxide.

The powder thus prepared is charged into a hopper 1 according to FIG. 1 below. Feeder 2 is at the bottom of hopper 1.
This feeder 2 is equipped with hydrogen (H2).
Gas is supplied, and the hydrogen gas transports the powders, which are fed into the plasma torch 4 installed at the top of the reactor 3. Although the drawing shows a ring-type plasma torch (for example, the plasma torch as described in Japanese Patent Application Laid-open No. 55-46266), it may also be used as a high-frequency induction heating plasma torch, or the reactor 3 may be used as a high-frequency induction heating plasma torch. It is possible to make it into a general arc reactor including an arc generating electrode as appropriate. The injected powder is 2000 yen generated from the plasma torch 4.
When hydrogen gas passes through a plasma gas stream at a temperature of .degree. C. or higher, the silicon dioxide constituting it is completely reduced mainly by the reducing agent carbon, producing silicon (St). The produced silicon is cooled together with the gas flow in a cooler 5, and reaches a separator 6; here, carbon monoxide (CO
), hydrogen (H2), water vapor (H2O), etc. are separated,
It will be collected.

<Function> As explained above, the main feature of the present invention is to pass a powder in which silicon dioxide and a reducing agent coexist integrally into plasma. Since each particle of the powder is composed of silicon dioxide and a reducing agent, it is possible to perform isothermal heating in which both are heated simultaneously under the same conditions. Furthermore, since the powder is supplied into an extremely high temperature plasma, silicon dioxide and the reducing agent can be brought to a high temperature of over 2000°C in an extremely short period of several milliseconds, resulting in intermediate carbonization. Suppresses the generation of silicon (SiC). And at this time,
When a hydrocarbon compound or a compound containing an oxygen atom is used as a reducing agent, these compounds, such as activated carbon and carbon black, start a reaction (a reaction in which the carbon atoms of the reducing agent combine with the oxygen atoms of silicon dioxide). (starting) requires more energy, but this ultimately results in
Silicon carbide (SiC) is generated during the process of heating silicon dioxide and reducing agent to a sufficient temperature, even if it is only for a very short time.
It works effectively to prevent the generation of Furthermore, since a powder containing silicon dioxide and a reducing agent coexisting together is supplied to the plasma, the silicon dioxide and the reducing agent always come into contact with each other on a large contact surface, and the carbon atoms of the reducing agent are exposed to silicon dioxide. The reaction of bonding with the oxygen atom progresses rapidly, resulting in the completion of the reduction reaction.

<Effects of the Invention> However, in the present invention, the slant-up function functions comprehensively, and to summarize, the following effects are obtained.

That is, when producing silicon by reducing silicon dioxide, highly pure silicon can be obtained efficiently and economically using simplified means.

Such effects of the present invention can be obtained by simply passing silicon dioxide powder into a hydrogen gas plasma, or by passing silicon dioxide powder into such a plasma, as will be described in more detail in the examples. This cannot be obtained simply by passing the powder and the powder of a reducing agent such as activated carbon or carbon black separately.

<Example> The following powders (in the case of the present invention, Comparative Examples-1 to Comparative Examples-3) were prepared, and each powder was subjected to reduction treatment under the following conditions according to FIG. Silicon (
The purity (%) of St) is shown in Table 1.

- In the case of the present invention: Silicon dioxide powder (purity 999%) that had been crushed and classified to about 200 to 350 mesh was added to a heated aqueous solution of saccharose at 50 to 70°C, and the mixture was sufficiently stirred and mixed to be kneaded. The ratio of silicon dioxide to saccharose was such that the molar ratio of silicon dioxide to the carbon component in sucrose was 1=2. The kneaded mixture was further dried at 150°C overnight, and then pulverized and classified to obtain a powder of 200 to 325 mesh.

- Comparative Example-1: In the case of the present invention example, the silicon dioxide used was similarly pulverized and classified to obtain a powder of 200 to 325 meshes.

・Comparative Example-2: Powder obtained by mixing the silicon dioxide powder obtained in Comparative Example-1 and activated carbon powder obtained by similarly crushing and classifying activated carbon using 200 to 325 mesh at a molar ratio of 1:2. I got it.

Comparative Example 3: Powder was obtained in the same manner as Comparative Example 2 except that carbon black was used instead of activated carbon.

Reduction treatment was carried out under the secondary condition-1 or condition-2.

Table 1 (Purity of St in recovered powder)

[Brief explanation of drawings]

FIG. 1 illustrates a system diagram of main parts in the present invention. 1...Hopper, 2...Feeder, 3...Reactor, 4...Plasma torch, 5.Cooler, 6.
...Separator, Attorney: Hiromasa Iriyama

Claims (1)

[Scope of Claims] A method for producing silicon, which comprises passing through plasma a powder in which silicon dioxide and a reducing agent coexist in the production of silicon by reducing silicon oxide. 2. The method for producing silicon according to claim 1, wherein the reducing agent is one or more selected from hydrocarbon compounds and compounds containing oxygen atoms. 3. The method for producing silicon according to claim 1 or 2, wherein the reducing agent contains sucrose. 4. The method for producing silicon according to claim 2 or 3, wherein the reducing agent is integrally co-existed in the powder so that the amount of carbon atoms is approximately 2 moles or more per mole of silicon dioxide.