Impurity directional migration and separation method based on molten metal silicon self-purification principle

Abstract

The invention relates to the technical field of impurity directional migration and separation, in particular to an impurity directional migration and separation method based on a molten metal silicon self-purification principle, which comprises the following steps of: putting a metal silicon raw material into a special quartz crucible with a zigzag concave-convex inner side wall, heating and vacuumizing to 1-100Pa by using a vacuum melting furnace, and injecting protective gas; when the temperature is raised to 1450-1750 DEG C, introducing specific gas from the bottom to promote the impurities to react and migrate, and keeping the temperature for 1-4 hours; and the crucible is controlled to descend, so that the silicon melt liquid is directionally solidified from bottom to top, the cooling speed is 30-50 DEG C / min, and the descending speed is 0.1-2 mm / min. And taking out the crucible after cooling, and cutting off the top and the adhesive part of the silicon ingot. The problems that in the prior art, directional migration and separation of impurities are difficult, solidification and segregation are difficult to control, crucible guiding is insufficient, and scientific control over slagging constituent matching and using is lacked are solved.

Description

Technical Field

[0001] This invention relates to the field of impurity directional migration and separation technology, specifically to an impurity directional migration and separation method based on the self-purification principle of molten silicon metal. Background Technology

[0002] Metallic silicon, also known as industrial silicon, is an important semiconductor material and strategic resource, playing a crucial role in modern industry. It is widely used in numerous fields. In the electronics industry, metallic silicon is a fundamental material for manufacturing semiconductor devices and integrated circuits; its purity directly affects the performance and stability of electronic products. In the photovoltaic industry, metallic silicon is a key raw material for preparing solar cells; high-purity metallic silicon can improve the photoelectric conversion efficiency of solar cells and reduce energy consumption. In aluminum alloy production, metallic silicon, as an important alloying element, can significantly improve the strength, hardness, and corrosion resistance of aluminum alloys, enhancing the quality and service life of aluminum alloy products. Therefore, improving the purity of metallic silicon is of great significance for promoting the development of related industries.

[0003] In existing silicon metal purification technologies, there are still significant challenges in the effective directional migration and separation of impurities. On the one hand, there is a lack of effective means to promote the migration of impurities from the silicon metal matrix, resulting in incomplete impurity removal. On the other hand, during the directional solidification process, it is difficult to precisely control the segregation effect of impurities, resulting in uneven distribution of impurities at the solid-liquid interface, which affects purification efficiency and quality.

[0004] Meanwhile, the existing quartz crucibles have a simple structure, and during the melting and solidification process, they lack effective guidance and control over the flow of molten silicon and the migration of impurities, which is not conducive to the directional migration and separation of impurities. Moreover, during the purification process, the use of slag-forming agents lacks scientific and reasonable proportioning and control, and cannot give full play to the role of slag-forming agents in assisting the removal of impurities. Summary of the Invention

[0005] The technical problem to be solved by this invention is that existing methods suffer from difficulties in the directional migration and separation of impurities, difficulty in controlling solidification and segregation, insufficient crucible guidance, and a lack of scientific control over the proportioning and use of slag-forming agents.

[0006] To solve the above problems, the technical solution adopted by the present invention is a method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon, comprising: placing metallic silicon raw material in a quartz crucible with a special structure, wherein the quartz crucible includes a crucible body and a serrated portion disposed on the inner side wall of the crucible body;

[0007] The metallic silicon in the quartz crucible was heated and evacuated using a vacuum melting furnace, with the vacuum level set to 1-100 Pa.

[0008] Inject protective gas into the vacuum melting furnace;

[0009] When the melting temperature rises to 1450℃-1750℃, a specific gas is introduced from the bottom of the quartz crucible to promote the reaction and migration of impurities, and the temperature is maintained for 1-4 hours.

[0010] The quartz crucible is controlled to descend, so that the high-purity silicon molten liquid gradually solidifies and purifies from bottom to top to obtain high-purity silicon ingots. The cooling rate during directional solidification is 30-50℃ / min, and the descent rate of the quartz crucible is 0.1-2mm / min.

[0011] After the quartz crucible has cooled, remove it and cut off the top of the high-purity silicon ingot and the part that is stuck to the quartz crucible.

[0012] As a further aspect of the present invention: the specific gas is chlorine, which reacts chemically with impurities in metallic silicon to generate volatile or easily separable substances, thereby promoting the migration of impurities from metallic silicon.

[0013] As a further aspect of the present invention: before placing the silicon metal raw material into the quartz crucible, the silicon metal raw material is pulverized to make its particle size uniform, which facilitates the subsequent melting and purification process.

[0014] As a further aspect of the present invention: before heating the silicon metal raw material in a vacuum melting furnace, a slagging agent is added to the silicon metal raw material. The slagging agent is sodium calcium silicate and may also contain alkali metal fluorides to help remove impurities from the silicon metal.

[0015] As a further aspect of the present invention, the amount of slag-forming agent added is 1%-5% of the mass of the silicon metal raw material, and can be appropriately adjusted according to the content and type of impurities in the silicon metal raw material.

[0016] As a further aspect of the present invention: during the directional solidification process, by precisely controlling the descent speed and cooling rate of the quartz crucible, the segregation effect of impurities at the solid-liquid interface is optimized, thereby improving the purification efficiency.

[0017] As a further aspect of the present invention: after removing the top of the high-purity silicon ingot and the portion that adheres to the quartz crucible, the remaining high-purity silicon ingot is subjected to surface treatment to remove any possible residual impurities and oxides, thereby improving the surface quality of the high-purity silicon ingot.

[0018] As a further aspect of the present invention, the method also includes quality testing of the purified high-purity silicon ingot, with testing indicators including silicon content, impurity element content, etc., to ensure that the purified high-purity silicon ingot meets the relevant standard requirements.

[0019] Compared with existing technologies, the advantages of this invention are as follows: Through the comprehensive application of multiple purification methods, various impurities in metallic silicon can be effectively removed, significantly improving the purity of metallic silicon. Compared with traditional purification methods, this method can produce metallic silicon with higher purity, meeting the stringent purity requirements of high-end industries such as electronics and photovoltaics. During directional solidification, precise control of process parameters optimizes the segregation effect of impurities, shortens the purification cycle, and improves production efficiency. Simultaneously, the specially structured quartz crucible and reasonable process flow design make the entire purification process smoother, reducing unnecessary operational steps and time waste; the dosage of slagging agent is optimized and controlled, reducing raw material waste. Moreover, this method uses conventional equipment and process conditions, eliminating the need for expensive special equipment and high-energy-consuming operations, reducing production costs and demonstrating high economic efficiency and market competitiveness. During the purification process, the emission of waste liquid and waste gas is reduced, minimizing environmental impact. In particular, through vacuum melting and the rational selection of protective gases, excessive reaction between metallic silicon and air is avoided, reducing oxide formation and aligning with the concept of green and environmentally friendly development. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a technical solution to address the existing problems mentioned in the background section.

[0022] Specialized crushing equipment is used to crush silicon metal raw materials. During the crushing process, various parameters of the equipment, such as rotation speed and feed rate, are strictly controlled to ensure that the silicon metal raw materials have uniform particle size. Uniform particle size helps the silicon metal raw materials to be heated and melted quickly and evenly in the subsequent melting process, avoiding the problem of uneven distribution of impurities due to local overheating or undercooling.

[0023] The pretreated silicon metal raw material is carefully placed in a quartz crucible with a special structure. The quartz crucible consists of a crucible body and serrated protrusions and concave parts set on the inner side wall of the crucible body. The design of the serrated protrusions and concave parts is not arbitrary. It can change the flow state of the silicon metal melt in the crucible during the subsequent melting and solidification process, so that the silicon metal melt forms a specific flow field when it flows along the serrated structure, creating favorable conditions for the directional migration of impurities.

[0024] A quartz crucible containing silicon metal raw material is placed into a vacuum melting furnace. The silicon metal in the quartz crucible is heated, and a vacuum pump is activated simultaneously to precisely control the vacuum level within the range of 1-100 Pa. Under this vacuum environment, the possibility of silicon metal reacting with the surrounding gas can be effectively reduced, avoiding the introduction of new impurities due to oxidation or other reactions. Subsequently, a protective gas, such as argon or other inert gas, is injected into the vacuum melting furnace to further isolate the air and create a pure environment for the melting of silicon metal.

[0025] Before placing the quartz crucible into the vacuum melting furnace and starting to heat the silicon raw material, a slagging agent is added to the silicon raw material. The slagging agent is sodium calcium silicate, and alkali metal fluorides may also be included depending on the actual situation. The amount of slagging agent added needs to be precisely controlled according to the quality of the silicon raw material, generally 1%-5% of the quality of the silicon raw material, and can be adjusted appropriately according to the content and type of impurities in the silicon raw material. The slagging agent will form slag during the high-temperature melting process. The slag has good adsorption properties and can adsorb impurities in the silicon and encapsulate the impurities in the slag.

[0026] When the melting temperature rises to 1450℃-1750℃, a specific gas, chlorine, is introduced from the bottom of the quartz crucible. Under high temperature conditions, the chlorine reacts violently with impurities in the metallic silicon, such as aluminum and iron, to generate volatile chlorides. These chlorides gradually volatilize during the melting process, thereby promoting the migration of impurities from the metallic silicon. The temperature is maintained for 1-4 hours to ensure that the impurities react fully with the chlorine, so that as many impurities as possible are converted into separable substances.

[0027] The quartz crucible is lowered to allow the high-purity silicon molten liquid to gradually solidify and purify from bottom to top, resulting in a high-purity silicon ingot. During the directional solidification process, the cooling rate is precisely controlled at 30-50℃ / min, and the descent speed of the quartz crucible is 0.1-2mm / min. By precisely controlling these two parameters, the segregation effect of impurities at the solid-liquid interface can be optimized. During the cooling process, impurities have low solubility in the solid phase and will gradually migrate into the liquid phase. The directional solidification method causes impurities to continuously accumulate in the liquid phase. As the solidification process proceeds, the impurities are concentrated at the top of the silicon ingot.

[0028] After the quartz crucible cools, it is carefully removed. The top of the high-purity silicon ingot and any parts adhering to the crucible are cut off, as these parts contain a high concentration of impurities. After removal, the remaining high-purity silicon ingot undergoes surface treatment using methods such as mechanical polishing and chemical cleaning to remove any remaining impurities and oxides, improving the surface quality of the high-purity silicon ingot. A comprehensive quality test is then performed on the purified high-purity silicon ingot, including indicators such as silicon content and impurity element content. Through professional testing equipment and methods, it is ensured that the purified high-purity silicon ingot meets relevant standards and satisfies the application needs of different fields.

[0029] The working principle of this invention is as follows: Uniformly sized silicon raw materials absorb heat more quickly and evenly during melting, resulting in a more uniform temperature distribution throughout the melt. This avoids uneven impurity diffusion caused by localized temperature differences, providing a favorable foundation for the directional migration of impurities. The serrated unevenness on the inner wall of the quartz crucible alters the flow path and flow field distribution of the molten silicon. During melting and solidification, the melt flowing along the serrated structure generates specific eddies and shear forces. These forces promote the directional migration of impurities within the melt, making them more easily aggregated in specific areas, facilitating subsequent separation and removal. Melting in a vacuum environment reduces the reactivity of silicon with surrounding gases (such as oxygen and nitrogen), minimizing oxidation and nitriding reactions, thus preventing the introduction of new impurities. The injection of a protective gas further isolates the air, providing a relatively pure environment for silicon melting and ensuring the smooth progress of the purification process. The slag-forming agent forms slag during high-temperature melting, and the chemical components in the slag interact physically and chemically with the impurities in the silicon. On the one hand, slag can encapsulate impurities through physical adsorption; on the other hand, certain components in the slag can react chemically with the impurities to form stable compounds. These compounds remain in the slag, and as the slag rises or sinks, the impurities are separated from the molten silicon. When chlorine gas is introduced, it exhibits strong oxidizing and reactivity at high temperatures. It can react with metallic impurities in silicon through redox reactions, oxidizing the impurities into corresponding chlorides. These chlorides are highly volatile and gradually volatilize into gases at the melting temperature, thus separating from the silicon and effectively removing the impurities. During directional solidification, the segregation effect of impurities at the solid-liquid interface is optimized by precisely controlling the cooling rate and the descent rate of the quartz crucible. Based on the difference in solubility of impurities in the solid and liquid phases, the solubility of impurities in the solid phase decreases during cooling, causing them to gradually migrate into the liquid phase. Directional solidification causes impurities in the liquid phase to continuously accumulate towards the top of the silicon ingot. As solidification proceeds, the impurities are concentrated in the top region of the silicon ingot, thereby improving the purity of the main body of the silicon ingot.

[0030] The present invention and its embodiments have been described above, and such description is not restrictive. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for the directional migration and separation of impurities based on the self-purification principle of molten metallic silicon, characterized in that, Includes the following steps: The metallic silicon raw material is placed in a quartz crucible with a special structure. The quartz crucible includes a crucible body and a serrated part provided on the inner side wall of the crucible body. The metallic silicon in the quartz crucible was heated and evacuated using a vacuum melting furnace, with the vacuum level set to 1-100 Pa. Inject protective gas into the vacuum melting furnace; When the melting temperature rises to 1450℃-1750℃, a specific gas is introduced from the bottom of the quartz crucible to promote the reaction and migration of impurities, and the temperature is maintained for 1-4 hours. The quartz crucible is controlled to descend, so that the high-purity silicon molten liquid gradually solidifies and purifies from bottom to top to obtain high-purity silicon ingots. The cooling rate during directional solidification is 30-50℃ / min, and the descent rate of the quartz crucible is 0.1-2mm / min. After the quartz crucible has cooled, remove it and cut off the top of the high-purity silicon ingot and the part that is stuck to the quartz crucible.

2. The method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon according to claim 1, characterized in that: The specific gas is chlorine. Chlorine reacts chemically with impurities in metallic silicon to generate volatile or easily separable substances, promoting the migration of impurities from metallic silicon.

3. The method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon according to claim 1, characterized in that: Before placing the silicon metal raw material into the quartz crucible, the raw material is crushed to make its particle size uniform, which facilitates the subsequent melting and purification process.

4. The method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon according to claim 1, characterized in that: Before heating the silicon metal raw material in a vacuum melting furnace, a slagging agent is added to the silicon metal raw material. The slagging agent is sodium calcium silicate and may also contain alkali metal fluorides to help remove impurities from the silicon metal.

5. The method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon according to claim 1, characterized in that: The amount of slag-forming agent added is 1%-5% of the mass of the silicon metal raw material, and can be adjusted appropriately according to the content and type of impurities in the silicon metal raw material.

6. The method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon according to claim 1, characterized in that: During directional solidification, the descent speed and cooling rate of the quartz crucible are precisely controlled to optimize the segregation effect of impurities at the solid-liquid interface and improve purification efficiency.

7. The method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon according to claim 1, characterized in that: After removing the top of the high-purity silicon ingot and the portion that adheres to the quartz crucible, the remaining high-purity silicon ingot undergoes surface treatment to remove any remaining impurities and oxides, thereby improving the surface quality of the high-purity silicon ingot.

8. The method for directional migration and separation of impurities based on the self-purification principle of molten metallic silicon according to claim 1, characterized in that: The method also includes quality testing of the purified high-purity silicon ingots, with testing indicators including silicon content and impurity element content, to ensure that the purified high-purity silicon ingots meet the relevant standard requirements.