RU2565198C1 - Purification of industrial silicon - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: removal of impurities from industrial silicon, in particular, of iron comprises fusing the charge in the crucible, silicon teeming and melt crystallization for pushing off of impurities. Prior to teeming iron content in silicon is defined. Teeming and crystallization are performed in inclined crucibles preheated to 400-600°C. The inclination angle of said crucibles relative to horizon in the range of 0-90 degrees is defined by the formula Φ = 400·Fe, where Φ is said inclination angle, degrees, Fe is iron content in silicon before teeming, wt %. Invention allows the production of silicon with iron content lower than 0.20 wt %.

EFFECT: higher purification degree.

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Description

The invention relates to the field of metallurgy, and in particular to the production of metals and alloys in ore-thermal electric furnaces, and can be used in the production of technical silicon.

A known method for producing technical silicon, including dosing of quartz or quartzite, carbon reducing agents, loading them into an electric furnace, carbothermic reduction of silicon, discharge of the melt from the furnace and oxidative refining (purification) of impurities (aluminum, calcium) and casting silicon onto ingots ( Elkin K.S., Zelberg B.I. et al. Silicon Production. Metallurgist Handbook. St. Petersburg: MANEB, 2013, 364 pp.).

In the process of production of industrial silicon, part of the metal oxides (iron, aluminum, calcium) introduced by quartzite and ashes of reducing agents is reduced and transferred to the melt. The presence of foreign metals in the silicon melt impairs its quality and consumer properties. Metals such as aluminum and calcium are removed from the melt by oxidative refining, but less active metals such as iron and titanium are not removed by oxidative refining.

The closest analogue to the present invention is a method of vacuum cleaning silicon, known from the application US 2007077191 A1, publ. 04/05/2007.

The method includes melting the charge in a crucible using electron beam heating and holding the melt to remove impurities, the process being carried out in three stages. At the first stage, oxidizing agents, such as water vapor, are introduced into the vacuum chamber to remove impurities whose vapor pressure is lower than the silicon vapor pressure. As a result, these impurities form compounds with high vapor pressure, which are removed at this stage of the process. Then, in a high vacuum, impurities having a vapor pressure higher than the silicon vapor pressure are removed, and in the third stage, directed melt crystallization is carried out to push the impurities, for example metals, into the last part of the crystallized volume, which is then removed.

The disadvantage of this method is the high energy consumption for the process of purification of silicon from impurities.

The basis of the invention is the task of improving the quality of silicon.

In this case, the technical result is the production of silicon with an iron content of less than 0.20 wt. %

The technical result is achieved due to the fact that in a method including melting a charge in a crucible, casting silicon and directing crystallization of a melt to displace impurities, the iron content is determined before casting silicon, and casting and crystallization of silicon are carried out in preheated inclined molds, the angle of inclination which relative to the horizon in the range of 0-90 ° is determined by the formula:

Φ = 400 Fe

Where:

Φ - the angle of the mold, deg .;

Fe is the iron content in silicon before casting, wt. %

To increase the yield of silicon with a minimum iron content, the molds are heated to a temperature of 400-600 ° C before casting silicon.

The method is as follows.

After the refining process and determination of the iron content are completed, molten silicon is poured into the mold assembled from refractory blocks, after the crystallization is completed, the ingot is removed from the mold, the iron content is determined by the height of the ingot and sorted by grade.

To prevent the production of silicon with a high iron content in silicon, more than 0.5 wt. %, due to segregation in the ingot, the size of the column of liquid silicon in the mold was changed due to the inclination of the mold. The angle of inclination was determined by the formula:

Ф = к · Fe, where:

F - the angle of the mold, deg .;

k = 400 - proportionality coefficient determined by statistical methods;

Fe is the iron content in silicon before casting, wt. %

The results of casting silicon into inclined molds are shown in table 1.

To increase the yield of the target grade of silicon with a minimum iron content, molds were preheated before casting silicon. The test results are presented in table 2.

When the mold is heated below 400 ° C, there is a slight increase in the amount of silicon grade up to 0.20 wt. % iron, when heated above 400 ° C, the yield of silicon of the highest grade increases. The optimum temperature for heating the mold before casting is a temperature of 400-600 ° C, which corresponds to the maximum production of a grade of silicon with a minimum iron content. At temperatures above 600 ° C, the steel frame of the mold lining loses its strength, which leads to mold failure.

Claims (1)

The method of purification of technical silicon, including melting the charge in a crucible, casting silicon and directional crystallization of the melt to displace impurities, characterized in that before the casting of silicon, the iron content is determined, and the casting and crystallization of silicon are carried out in preheated to a temperature of 400-600 ° C inclined molds, the angle of inclination of which relative to the horizon in the range of 0-90 ° is determined by the formula:
Ф = 400 · Fe, where:
F - the angle of the mold, deg .;
Fe is the iron content in silicon before casting, wt. %