JPH04231316A - Decarburization method of metal silicon - Google Patents

Abstract

PURPOSE:To decrease the cost for decarburization by heating a filter vessel packed with a filter of a specified material and having through holes in its bottom comprising the same material as the filter material to over the melting point of Si, and supplying molten Si thereto while supplying O2-contg. gas through the bottom holes. CONSTITUTION:A filter vessel 1 is packed with a filter material essentially comprising silicon compd. such as quartz in spheres of >=5mm diameter, for example, as a packing layer 3. The filter vessel essentially consists of a silicon compd. such as quartz and has holes 4 in its bottom. Then the filter vessel 1 is heated to >=1410 deg.C which is the melting point of Si, and maintained that temp., while O2-contg. gas such as O2-Ar mixture gas is supplied as the counter flow through the bottom holes. Molten Si is supplied from the upper side of the packing layer 3 at a specified flow rate to obtain metal Si from which C is enough removed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for purifying silicon metal.

0002

BACKGROUND OF THE INVENTION In recent years, a method of reducing high-purity silica with high-purity carbon has been developed as a method for producing high-purity silicon at low cost. However, in this method of using carbon as a reducing agent, the produced silicon contains 5
00 to 1000 ppmw of carbon is contained. Therefore, a method for removing carbon from silicon is required.

Carbon exists in silicon in two forms: dissolved carbon (C) dissolved in silicon and silicon carbide (SiC) in which carbon with a saturated solubility or higher is precipitated. As a method for removing this carbon, Japanese Patent Application Laid-Open No. 64-56312 and Japanese Patent Application Laid-Open No. 1-17
As shown in Publication No. 6211, etc., filtration and sedimentation separation are known to be effective methods for SiC, but it has been difficult to remove C. On the other hand, regarding the removal of C, it has been found that the method of reducing pressure or supplying oxygen to molten silicon to promote the reaction of C+O→CO↑ and removing it as CO gas is effective, but it is relatively laborious and This is a time-consuming method.

0004

[Problems to be Solved by the Invention] As described above, in the prior art, a method was adopted in which SiC was first removed by filtration, sedimentation, etc., and then C was removed by depressurization and oxygen supply. , it was taking too long. There is also a method of directly performing unidirectional coagulation after filtration and sedimentation separation to lower the carbon concentration, but this method has a low yield and high cost, and cannot be said to be an advantageous method.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for decarburizing metallic silicon containing carbon relatively easily, in a short time, and at low cost.

[0006]

[Means for Solving the Problems] That is, the present invention has a through hole in the bottom and is provided with a filter material containing a substance mainly composed of a silicon compound in a filtration container made of a substance mainly composed of a silicon compound. This is a method for decarburizing metallic silicon, characterized in that molten silicon is supplied while the filter material is heated and held above the melting point of silicon, and an oxygen-containing gas is supplied from the bottom of the filtration container.

[0007]

[Operation] In the present invention, a container made of a substance mainly composed of silicon, oxygen, nitrogen, and carbon, such as quartz, silicon carbide, and silicon nitride, and a filler layer that acts as a filter are heated to a temperature higher than the melting point of silicon, for example. The temperature is maintained at 1,410 to 1,650°C, and molten silicon is passed through the filling layer.At the same time, gas containing oxygen is flowed through the filling layer from the bottom of the container in countercurrent or cocurrent.As a result, at the same time as SiC filtration, C+O→C
A reaction O↑ occurs, and carbon in silicon can be removed.

[0008] In order to filter SiC by passing the silicon through the filler layer, the silicon must be in a molten state, and it is necessary to heat and maintain the silicon at a temperature of 1410° C. or higher, which is the melting point of silicon. On the other hand, high temperatures are more advantageous in order to promote the C+O→CO↑ reaction, but there is a temperature limit that the packing material and filtration container can withstand;
It is desirable to process at a temperature of 650°C or less. If 1
If the temperature exceeds 650°C, the life of the filler layer will be shortened.

[0009] The material of the filler is preferably one whose main component is a substance that does not contaminate silicon or an element that can be easily removed even if it contaminates silicon. The shape of the filler includes spheres, tubes, particles, fibers, etc., but other shapes can be used as long as they do not significantly prevent the passage of molten silicon and gas. In order to improve the passage of gas and molten silicon, it is desirable to have a diameter of 5 mm or more. Also, instead of a filler layer, a stack of plates with holes drilled therein can be used.

[0010] As the gas to be brought into contact with silicon in the filler layer, any gas containing oxygen such as O2, Ar-O2, H2O, air, etc. can be used, and a high purity gas is desirable in order not to contaminate silicon. . It is desirable to supply the oxygen-containing gas through the hole at the bottom of the container, as shown in Figure 1.
A gas blowing hole may be provided in the container wall near the bottom of the container, and the gas may be blown horizontally into the filter material.

[0011] Furthermore, if oxygen is a component of the container and the filler layer and sufficient oxygen is supplied to silicon, an oxygen-free gas may be supplied. This method is carried out under atmospheric pressure, but in order to advance the decarburization reaction, it is advantageous to lower the CO partial pressure and increase the oxygen partial pressure in the atmosphere, and even better results can be obtained when carried out under reduced pressure. Although this is somewhat disadvantageous in extracting CO gas from silicon, the decarburization reaction proceeds sufficiently even if a certain amount of pressure is applied.

[0012] Regarding the removal of SiC contained in silicon, most of it is removed at the surface layer of the filler layer, and the filler layer acts as a filter material for surface filtration.

[0013]

[Example] Example 1 A quartz container with an inner diameter of 100 mm was filled with quartz grains with a particle diameter of 10 mm as a filter material to a thickness of 200 mm.
%H2O-90%Ar was passed from bottom to top at 10 l/min in countercurrent to silicon as shown in Figure 1.
The temperature was maintained at 00°C.

[0014] The average carbon concentration on this filler layer is 2000p.
pmw of silicon in 10 minutes, 20kg, 10kg, 5
When passing through 2.5 kg and 2.5 kg, the average carbon concentration was 50 ppmw, 40 ppmw, and 30 p, respectively.
pmw, decreased to 20ppmw. Comparative Example 1 Using the same container and filler layer as in Example 1, 20 kg, 10 kg of silicon was heated for 10 minutes at the same temperature without passing gas.
g, 5kg, 2.5kg When processed, 70,70
, 70, the carbon concentration decreased only to 60 ppmw.

[0015] As described above, silicon having a carbon concentration as low as that in the conventional method can be easily obtained by a treatment similar to the conventional filtration treatment.

[0016]

[Effects of the Invention] According to the present invention, silicon can be easily decarburized and silicon can be produced at a lower cost.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one example of a filtration container used in the present invention.

[Explanation of symbols]

1. Filtration container 2 Molten silicon 3 Filler layer 4 Container bottom through hole 5 Oxygen-containing gas 6 Heater

Claims (1)

[Claims] Claim 1: A filtration container having a through hole in the bottom and made of a substance containing a silicon compound as its main component is filled with a substance containing a silicon compound as a filter material, and the filter material is filled with silicone. 1. A method for decarburizing metallic silicon, which comprises supplying molten silicon while keeping it heated above its melting point, and supplying an oxygen-containing gas from the bottom of the filtration vessel.