CN109970068B - Method for purifying polycrystalline silicon by high-entropy alloy - Google Patents

Abstract

The invention relates to a method for purifying polycrystalline silicon by using high-entropy alloy, belonging to the field of high-crystalline silicon purification. The method for purifying the polycrystalline silicon by using the high-entropy alloy comprises the following steps: a. mixing the high-entropy alloy with a raw material silicon, heating to be molten in vacuum or inert atmosphere, and performing directional solidification under an electromagnetic field; b. and cooling after directional solidification, and separating silicon from the alloy to obtain purified polycrystalline silicon. According to the method, the high-entropy alloy phase is separated from the silicon phase by using the vacuum electromagnetic induction furnace and the directional solidification device, so that the wear resistance of the alloy is improved while boron in the silicon is removed, and a new thought is provided for a low-cost preparation technology of solar-grade silicon in a boron removal link.

Description

Method for purifying polycrystalline silicon by high-entropy alloy

technical field

The invention relates to a method for purifying polycrystalline silicon by utilizing a high-entropy alloy, and belongs to the field of high-crystalline silicon purification.

Background technique

At present, solar-grade polysilicon (6N) is mainly doped with semiconductor-grade silicon (9N) produced by the modified Siemens method. Although the average cost of polysilicon manufactured by the improved Siemens method has dropped from US$70/kg in 2007 to US$12/kg in 2017 with the breakthrough of key technologies and the reduction of energy consumption, in order to ensure the best current transfer rate of the battery, The Siemens method also requires a doping process, which undoubtedly wastes purity and increases manufacturing costs.

Another method: metallurgical method, which has the advantages of low energy consumption, environmental friendliness, sustainable production and other advantages, has huge market potential, and is becoming a global research hotspot. Metallurgical method directly purifies industrial grade silicon (2-3N) to solar grade silicon (6N) through slag refining, wet leaching, vacuum evaporation, directional solidification, electron beam and plasma refining and other impurity removal technologies. According to the "Dongmeng Method" of Ningxia Dongmeng Energy Co., Ltd., its technological process is characterized as shown in Figure 1, specifically: in the slag-making step of the submerged arc furnace, the solubility of some impurities in the mixed state of metal silicon liquid and slag liquid is utilized. In the physical crushing step, the principle of segregation of impurities in silicon (the fixed form of impurities existing in metallic silicon) is used to remove specific impurities such as B, Al, Ca, etc. Physical separation of impurities and silicon is achieved in the hydrometallurgy step; in the hydrometallurgical step, the impurities attached to the surface of the silicon material with small particle size and large surface area are subjected to acid leaching to remove most of the metal impurities; in the electron beam melting step: the use of electron beams The principle of a large number of supplementary electrons and the characteristics of high temperature gasification are used to achieve deep removal of phosphorus, iron and oxygen under high vacuum; the final product is finished. The main problems of the "Dongmeng method" are: 1. The solubility is limited, and the boron removal effect is unstable; 2. The efficiency of the slag system is reduced for many times.

Among impurities in silicon, metal impurities can be removed by hydrometallurgy, electron beam, and directional solidification; phosphorus impurities can be removed by vacuum distillation; but boron element has a segregation coefficient (0.8) and a low saturated vapor pressure (1823K) similar to silicon. , is 6.78×10 ^-7 Pa), which is difficult to remove by the above method. Once the boron content in solar-grade polysilicon exceeds 0.3ppmw, it will form BO defects with interstitial oxygen and recombine with electrons or holes to form a deep energy level, reducing the lifetime of minority carriers and thus affecting its photoelectric conversion efficiency. In addition, the content of impurity boron in silicon is extremely low (10-30ppmw), and its activity is very small, which also increases the difficulty of its removal.

At present, researchers at home and abroad mainly use four methods to refine and remove boron, namely slag refining, alloy refining, air-blown refining and plasma refining. However, due to the disadvantages of expensive vacuum plasma equipment, complicated operation, low output, and explosiveness, mass production is impossible. Air-blown refining is to refine silicon liquid by means of ventilation. Although it has a good removal effect on C, O, B, etc., it is not easy to fully contact with impurities, so the removal effect is poor; the slag-making process is to melt silicon first, then Adding alkaline oxides and acidic oxides to adsorb impurities in the silicon liquid into the slag, this process has a little effect on B but has its limit. The traditional alloy method was proposed by Professor Yoshikawa of Tokyo University in 2005 to remove boron impurities in silicon by using Si-Al alloy directional solidification method. Later, researchers used Si-Al-Sn, Si-Sn, Cu-Si and other alloys to remove boron impurities. However, there are two problems with the above-mentioned traditional silicon-aluminum, silicon-tin and other alloying methods: 1. If the directional solidification is carried out in an ordinary resistance furnace instead of an electromagnetic induction furnace, the silicon phase and the alloy phase cannot be separated; in Si-Al In the alloying method, according to the thesis of the founder of the alloying method, Professor Yoshikawa Ken, it can be seen that the alloy can only be formed by resistance heating, and the alloy phase can be separated from the silicon phase only under the premise of induction heating due to electromagnetic stirring. The same is true for Si-Sn. According to the article published by the Chinese Academy of Sciences and my experiments, the separation method is to digest the alloy phase with hydrochloric acid, leaving the pure silicon phase. This is the most effective separation method at present, so the alloy can only be used once and cannot be used repeatedly, which is also the bottleneck restricting its application. 2. To effectively remove boron impurities, the proportion of aluminum and tin needs to be large. Therefore, after directional solidification, silicon-aluminum and silicon-tin alloys with a mass ratio of more than 70% will be formed. Pure silicon often has only a small part, and the silicon yield very low.

It is difficult to use a certain method alone to meet the requirements of solar-grade silicon for impurity boron content. Although domestic and foreign researchers have tried coupling methods such as slagging-air blowing, slagging-alloying, slag-forming-pickling, etc., they have achieved certain results. However, due to the problems of high energy consumption, poor stability and high cost, and the B removal effect obtained by different researchers is very different, the content of B in silicon is reduced to the standard of polysilicon for solar cells (less than 0.3ppmw) There is still some difficulty. In summary, in order to overcome the limitations of the above four methods, it is urgent to find a method, which can improve the distribution ratio of boron in the alloy phase and the silicon phase, simplify the steps, and achieve deep, effective, low-cost removal The purpose of boron.

On the other hand, since Professor Ye Junwei proposed the concept of "high-entropy alloy" in 2004, more and more researchers have found that when there are five or more metal or non-metallic elements with equal components in the alloy It is a new type of solid solution alloy with four characteristics: (1) high entropy effect to form a simple solid solution without intermediate compounds; (2) slow diffusion effect; (3) severe lattice distortion; (4) cocktail effect. The developed high-entropy alloys exhibit high strength and hardness, excellent wear and corrosion resistance, and good high temperature stability. It has received extensive attention from scholars in the field of materials science and engineering.

In terms of the preparation process of high-entropy alloys, the commonly used methods for preparing high-entropy alloy bulk include: vacuum melting, spark plasma sintering, powder metallurgy, mechanical alloying, laser 3D printing, directional solidification, etc. The periodic table positions of high-entropy alloy elements can be roughly divided into two categories: one is a low-melting alloy system composed of CoCrFeNi-(A1, Ti, Cu, Mn) metal elements; the other is Ti, Nb, Ta , Mo, W and other high melting point metal elements composed of high melting point high entropy alloy system. At present, there is no report on polysilicon purification using high-entropy alloys.

SUMMARY OF THE INVENTION

In view of the above defects, the technical problem solved by the present invention is to provide a method for purifying polysilicon by using high-entropy alloy. Boron impurities in silicon can be reduced in a short processing time using a simple method.

The invention utilizes the body-centered cubic structure of the high-entropy alloy to absorb boron and other difficult-to-remove impurities in silicon; and utilizes a vacuum electromagnetic induction furnace and a directional solidification device to realize the separation of the high-entropy alloy phase and the silicon phase. The schematic diagram of directional solidification induction refining of the high-entropy alloy of the present invention and the principle diagram of alloy solidification refining are shown in Figure 2 of the description. Wherein, the high-entropy alloy refers to an alloy formed of five or more metals in equal or approximately equal amounts.

The method for purifying polysilicon using high-entropy alloy includes the following steps:

a. Mix the high-entropy alloy with the raw material silicon, heat it to melt in a vacuum or an inert atmosphere, and conduct directional solidification under an electromagnetic field;

b. Cooling after directional solidification, separating silicon and alloy to obtain purified polysilicon.

Wherein, the polycrystalline silicon of the present invention can be industrial grade silicon or polycrystalline silicon.

In step a, the high-entropy alloy and the raw material silicon can be mixed in a crucible, preferably, the material of the crucible is graphite or corundum. The crucible is then placed in a heating device for heating, preferably, the heating device is an intermediate frequency induction heating furnace.

Further, in order to shorten the separation time of the alloy phase and the silicon phase and improve the separation effect, in step a, before the high-entropy alloy is mixed with the raw material silicon, the high-entropy alloy is pretreated, and the pretreatment method is: Warm to melting under vacuum or inert atmosphere, then furnace cool to room temperature.

Since high melting point high entropy alloys usually use high melting point noble metals, such as Ti, Nb, Ta, Mo, W and other noble metals. In order to save cost, the high-entropy alloy used in the present invention is a low-melting point high-entropy alloy. Preferably, the melting point of the high-entropy alloy is less than or equal to the melting point of silicon. The melting point of silicon is about 1420°C.

Further, in step a, the high-entropy alloy is composed of five elements; in order to further reduce the content of B in the polysilicon, preferably, the high-entropy alloy is composed of five elements of Co, Cr, Fe, Ni and Al, or the high-entropy alloy is composed of five elements. Consists of five elements of Co, Cr, Fe, Ni and Ti, or high-entropy alloys are composed of five elements of Co, Cr, Fe, Ni and Cu, or high-entropy alloys are composed of five elements of Co, Cr, Fe, Ni and Mn The element composition, or the high-entropy alloy is composed of five elements of Al, Fe, Ni, Ti and Cu; further preferably, the entropy alloy is composed of five elements of Al, Fe, Ni, Ti and Cu;

More preferably, the molecular formula of the high-entropy alloy is AlFeNiTiCu, CoCrFeNiAl, CoCrFeNi _0.5 Cu _1.5 , and CoCrFeNiMn; most preferably, the molecular formula of the high-entropy alloy is AlFeNiTiCu.

Further, in step b: the purity of the raw material silicon is not less than 99wt%.

The addition amount of the high-entropy alloy will affect the removal efficiency of impurities. Further, in step b: the mass ratio of the high-entropy alloy to the raw silicon is 5:1 to 1:5; the preferred mass ratio of the high-entropy alloy to the raw silicon is 1 : 2 to 2:1, more preferably, the mass ratio of the high-entropy alloy to the raw material silicon is 1:1.

Further, in step a: the inert gas is argon or nitrogen.

The gas flow rate of the present invention is related to the weight of the raw material silicon. Further, in step a: per gram of the raw material silicon, the flow rate of the injected inert gas is 15-30 mL/min; preferably, per gram of the raw material silicon , the flow rate of the blown inert gas is 20mL/min.

The present invention can be realized by the temperature at which the raw silicon is melted. In order to better purify and ensure the rate of chemical reaction and the good fluidity of the slag, further, in step a: the heating temperature is 1250-1550°C.

The directional solidification speed of the present invention is theoretically as slow as possible, but too slow will increase production time, and too fast will not separate phases, and silicon and alloy cannot be separated. Therefore, in step b, the directional solidification speed is preferably 1 mm/h to 10 mm/h.

Further, in step b, the cooling method is airtight cooling or normalizing cooling.

Beneficial effects of the present invention:

1. The present invention uses high-entropy alloy to purify polycrystalline silicon, and innovatively proposes to use a new type of high-entropy alloy material to remove boron impurities in industrial silicon in the process of polycrystalline silicon purification. Taking advantage of the solid solution structure and slow diffusion characteristics of high-entropy alloys, in high-temperature melting and directional solidification, crystalline silicon is preferentially precipitated, and the impurity boron is enriched into the high-entropy alloy phase according to the principle of segregation, so that the boron impurities in crystalline silicon are greatly reduced. Purpose. The separation principle of high-entropy alloys to purify polysilicon is not only that the Me-B interaction coefficient of the traditional alloy method is greater than that of Si-B, so that B will move from silicon to the alloy, it will also form a simple FCC face center in structure. Cubic structure solid solution, so that the B element can be easily transferred into the high-entropy alloy phase.

2. Compared with the traditional alloying method, due to the high entropy characteristics, the alloying elements first form an alloy without reacting with silicon, which saves silicon raw materials; while the traditional alloying method will react with silicon, resulting in a large loss of silicon raw materials .

3. By combining advanced material high-entropy alloy and directional solidification method under electromagnetic field, the present invention breaks through the limitation of removing boron impurities by a single method, and improves the wear resistance of the alloy while realizing the removal of boron from silicon, so as to prepare solar energy at low cost. High-grade silicon technology provides new ideas in boron removal.

4. The traditional alloy method reduces the efficiency of reuse due to the increase of B impurity content after the test, while the high entropy alloy will improve its wear resistance because of the B element, which can be used in welding, bearings, wear-resistant coatings, golf clubs Ball head and other industries.

5. The method of the present invention has simple steps, high boron removal efficiency and low cost.

6. The polysilicon purified by the method of the present invention has a boron removal rate of more than 90% and a polysilicon yield of more than 80%; when the high-entropy alloy AlFeNiTiCu is used for processing, the boron removal rate is 99.4%, and the polysilicon yield is 82%. , the B content in the obtained polysilicon is 0.3ppmw, which meets the requirements of solar grade silicon.

Description of drawings

Figure 1 is the technological process of "Dongmeng method";

In Fig. 2, a is a schematic diagram of the directional solidification induction refining of the present invention; b is a schematic diagram of alloy solidification refining, and the small black dots in the figure b represent B impurities.

Detailed ways

In view of the above defects, the technical problem solved by the present invention is to provide a method for purifying polysilicon by using high-entropy alloy. Boron impurities in silicon can be reduced in a short processing time using a simple method.

The invention utilizes the body-centered cubic structure of the high-entropy alloy to absorb boron and other difficult-to-remove impurities in silicon; and utilizes a vacuum electromagnetic induction furnace and a directional solidification device to realize the separation of the high-entropy alloy phase and the silicon phase. The schematic diagram of directional solidification induction refining of the high-entropy alloy of the present invention and the principle diagram of alloy solidification refining are shown in Figure 2 of the description. Wherein, the high-entropy alloy refers to an alloy formed of five or more metals in equal or approximately equal amounts.

The method for purifying polysilicon using high-entropy alloy includes the following steps:

a. Mix the high-entropy alloy with the raw material silicon, heat it to melt in a vacuum or an inert atmosphere, and conduct directional solidification under an electromagnetic field;

b. Cooling after directional solidification, separating silicon and alloy to obtain purified polysilicon.

Wherein, the polycrystalline silicon of the present invention can be industrial grade silicon or polycrystalline silicon, and the content of B in the raw silicon is 10-50 ppmw; preferably, the content of B in the raw silicon is 30-50 ppmw.

In step a, the high-entropy alloy and the raw material silicon can be mixed in a crucible, preferably, the material of the crucible is graphite or corundum. The crucible is then placed in a heating device for heating, preferably, the heating device is an intermediate frequency induction heating furnace.

Further, in order to shorten the separation time of the alloy phase and the silicon phase and improve the separation effect, in step a, before the high-entropy alloy is mixed with the raw material silicon, the high-entropy alloy is pretreated, and the pretreatment method is: Warm to melting under vacuum or inert atmosphere, then furnace cool to room temperature.

Since high melting point high entropy alloys usually use high melting point noble metals, such as Ti, Nb, Ta, Mo, W and other noble metals. In order to save cost, the high-entropy alloy used in the present invention is a low-melting point high-entropy alloy. Preferably, the melting point of the high-entropy alloy is less than or equal to the melting point of silicon. The melting point of silicon is about 1420°C.

Further, in step a, the high-entropy alloy is composed of five elements; in order to further reduce the content of B in the polysilicon, preferably, the high-entropy alloy is composed of five elements of Co, Cr, Fe, Ni and Al, or the high-entropy alloy is composed of five elements. Consists of five elements of Co, Cr, Fe, Ni and Ti, or high-entropy alloys are composed of five elements of Co, Cr, Fe, Ni and Cu, or high-entropy alloys are composed of five elements of Co, Cr, Fe, Ni and Mn The element composition, or the high-entropy alloy is composed of five elements of Al, Fe, Ni, Ti and Cu; further preferably, the entropy alloy is composed of five elements of Al, Fe, Ni, Ti and Cu;

More preferably, the molecular formula of the high-entropy alloy is AlFeNiTiCu, CoCrFeNiAl, CoCrFeNi _0.5 Cu _1.5 , and CoCrFeNiMn; most preferably, the molecular formula of the high-entropy alloy is AlFeNiTiCu.

Further, in step b: the purity of the raw material silicon is not less than 99wt%.

The addition amount of the high-entropy alloy will affect the removal efficiency of impurities. Further, in step b: the mass ratio of the high-entropy alloy to the raw silicon is 5:1 to 1:5; the preferred mass ratio of the high-entropy alloy to the raw silicon is 1 : 2 to 2:1, more preferably, the mass ratio of the high-entropy alloy to the raw material silicon is 1:1.

Further, in step a: the inert gas is argon or nitrogen.

The gas flow rate of the present invention is related to the weight of the raw material silicon. Further, in step a: per gram of the raw material silicon, the flow rate of the injected inert gas is 15-30 mL/min; preferably, per gram of the raw material silicon , the flow rate of the blown inert gas is 20mL/min.

The present invention can be realized by the temperature at which the raw silicon is melted. In order to better purify and ensure the rate of chemical reaction and the good fluidity of the slag, further, in step a: the heating temperature is 1250-1550°C.

The directional solidification speed of the present invention is theoretically as slow as possible, but too slow will increase production time, and too fast will not separate phases, and silicon and alloy cannot be separated. Therefore, in step b, the directional solidification speed is preferably 1 mm/h to 10 mm/h.

Further, in step b, the cooling method is airtight cooling or normalizing cooling.

Among them, after directional solidification and cooling, the obtained product has an obvious interface between the alloy phase and the silicon phase. According to the interface, the silicon and the alloy are separated by cutting and separating with a steel stone.

The specific embodiments of the present invention will be further described below with reference to the examples, but the present invention is not limited to the scope of the described examples.

Wherein, the yield calculation formula in the following examples and comparative examples is: yield=mass of pure silicon obtained after cutting/mass of initial silicon.

Example 1

1) Weigh 5g of raw material industrial grade silicon with impurity boron content of 50ppmw, and weigh a total of 5g of high-purity alloy powder according to the AlFeNiTiCu ratio of equal molar ratio.

2) Under an argon atmosphere, AlFeNiTiCu was pre-melted at 1250°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1250° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace. The pull-down speed is 1 mm/h. The silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and alloy were cut and separated by stainless steel. The yield of polysilicon was 82.1%. After sampling, digestion was carried out for ICP detection. The boron content was reduced to 0.3ppmw, and the alloy phase boron content was increased to 48.7ppmw.

Example 2

1) Weigh 10 g of raw material industrial grade silicon with an impurity boron content of 50 ppmw, and weigh a total of 5 g of high-purity alloy powder according to the AlFeNiTiCu ratio of equal molar ratio.

2) Under an argon atmosphere, AlFeNiTiCu was pre-melted at 1300°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1300° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace, and the pull-down speed is 10mm/h, the silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy were cut and separated by fine steel. The yield of polysilicon was 84.7%. After sampling, digestion was carried out for ICP detection. The boron content was reduced to 0.9ppmw, and the alloy phase boron content was increased to 48.9ppmw.

Example 3

1) Weigh 5g of raw material industrial-grade silicon with impurity boron content of 10ppmw, and weigh 5g of high-purity alloy powder according to the AlFeNiTiCu ratio of equal molar ratio.

2) Under an argon atmosphere, AlFeNiTiCu was pre-melted at 1250°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1250° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace. The pull-down speed is 1 mm/h. The silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy are cut and separated by stainless steel. The yield of polysilicon is 80.3%. After sampling, digestion is carried out for ICP detection. The boron content is reduced to 0.28ppmw, and the alloy phase boron content is increased to 0.71ppmw.

Example 4

5g of raw material industrial grade silicon with impurity boron content of 50ppmw was weighed, and 1g of high-purity alloy powder was weighed according to the AlFeNiTiCu ratio of equal molar ratio, and other operations were the same as in Example 1. The yield of polysilicon prepared in this example was 94.1%. After sampling, digestion was carried out for ICP detection. The boron content decreased to 4.5 ppmw, and the alloy phase boron content increased to 45.6 ppmw.

Example 5

Weigh 5 g of raw material industrial grade silicon with impurity boron content of 50 ppmw, and weigh a total of 25 g of high-purity alloy powder according to the AlFeNiTiCu ratio with equal molar ratio, and other operations are the same as in Example 1. The yield of polysilicon prepared in this example was 82.6%. After sampling, digestion was carried out for ICP detection. The boron content was reduced to 0.28 ppmw, and the alloy phase boron content was increased to 48.6 ppmw.

Example 6

1) Weigh 5 g of raw silicon with a boron content of 50 ppmw, and weigh a total of 5 g of metal powder according to CoCrFeNiAl having an equal molar ratio.

2) Under an argon atmosphere, CoCrFeNiAl was pre-melted at 1450°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1450° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace, and the pull-down speed is 5mm/h, the silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy were cut and separated by fine steel. The yield of polysilicon was 90.2%. After sampling, digestion was carried out for ICP detection. The boron content was reduced to 2.7ppmw, and the alloy phase boron content was increased to 47.0ppmw.

Example 7

1) Weigh 5 g of raw silicon with a boron content of 50 ppmw, and weigh a total of 10 g of metal powder according to CoCrFeNiAl having an equal molar ratio.

2) Under an argon atmosphere, CoCrFeNiAl was pre-melted at 1500°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1500° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace. The pull-down speed is 1 mm/h. The silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy are cut and separated by steel stone. The yield of polysilicon is 88.3%. After sampling, digestion is carried out for ICP detection. The boron content is reduced to 1.4ppmw, and the alloy phase boron content is increased to 48.2ppmw.

Example 8

1) Weigh 5 g of raw silicon with a boron content of 50 ppmw, and weigh a total of 5 g of metal powder according to CoCrFeNi _0.5 Cu _1.5 with an equal molar ratio.

2) Under an argon atmosphere, CoCrFeNi _0.5 Cu _1.5 was pre-melted at 1500°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1500° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace, and the pull-down speed is 2mm/h, the silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and alloy were cut and separated by stainless steel. The yield of polysilicon was 91.7%. After sampling, digestion was carried out for ICP detection. The boron content was reduced to 1.8ppmw, and the alloy phase boron content was increased to 47.5ppmw.

Example 9

1) Weigh 5 g of raw silicon with a boron content of 50 ppmw, and weigh a total of 10 g of metal powder according to CoCrFeNi _0.5 Cu _1.5 with an equal molar ratio.

2) Under an argon atmosphere, CoCrFeNi _0.5 Cu _1.5 was pre-melted at 1500°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1500° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace, and the pull-down speed is 8 mm/h, the silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy are cut and separated by stainless steel. The yield of polysilicon is 91.0%. After sampling, digestion is carried out for ICP detection. The boron content is reduced to 2.9ppmw, and the alloy phase boron content is increased to 46.5ppmw.

Example 10

1) Weigh 5 g of raw silicon with a boron content of 50 ppmw, and weigh a total of 5 g of metal powder according to CoCrFeNiMn having an equal molar ratio.

2) Under an argon atmosphere, CoCrFeNiMn was pre-melted at 1550°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1550° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace, and the pull-down speed is 10mm/h, the silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and alloy are cut and separated by stainless steel, and after sampling, they are digested and tested by ICP. The boron content is reduced to 4.8ppmw, and the alloy phase boron content is increased to 44.5ppmw.

Example 11

1) Weigh 5 g of raw silicon with a boron content of 50 ppmw, and weigh a total of 10 g of metal powder according to CoCrFeNiMn having an equal molar ratio.

2) Under an argon atmosphere, CoCrFeNiMn was pre-melted at 1550°C and cooled to an ingot.

3) Mix the pre-melted alloy with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1550° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace, and the pull-down speed is 5mm/h, the silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy are cut and separated by fine steel. The yield of polysilicon is 89.4%. After sampling, digestion is carried out for ICP detection. The boron content is reduced to 3.1ppmw, and the alloy phase boron content is increased to 46.5ppmw.

Comparative Example 1

1) Weigh 5g of raw material industrial grade silicon with impurity boron content of 50ppmw, and weigh 5g of high-purity Sn powder in total.

2) Under an argon atmosphere, the Sn powder was pre-melted at 1250°C and cooled to an ingot.

3) Mix the pre-melted Sn with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1250° C. under an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace. The pull-down speed is 1 mm/h. The silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy are cut and separated by stainless steel. The yield of polysilicon is 37.1%. After sampling, digestion is carried out for ICP detection. The boron content is reduced to 3.62ppmw, and the alloy phase boron content is increased to 46.2ppmw.

Comparative Example 2

1) Weigh 5g of raw material industrial grade silicon with impurity boron content of 50ppmw, and weigh 5g of high-purity Al powder in total.

2) Under an argon atmosphere, the Al powder was pre-melted at 1250°C and cooled to an ingot.

3) Mix the pre-melted Al with industrial silicon, put it into a graphite crucible, place it in an electromagnetic induction heating furnace, and melt it at 1250° C. in an argon atmosphere.

4) After being completely melted, directional solidification is carried out in an induction furnace. The pull-down speed is 1 mm/h. The silicon is precipitated first, the alloy phase is precipitated later, and it is normalized and cooled.

5) The silicon and the alloy are cut and separated by stainless steel. The yield of polysilicon is 35.7%. After sampling, digestion is carried out for ICP detection. The boron content is reduced to 2.63ppmw, and the alloy phase boron content is increased to 47.2ppmw.

Claims (21)

1. the method that utilizes high entropy alloy to purify polysilicon, is characterized in that, comprises the steps: a. Mix the high-entropy alloy with the raw material silicon, heat it to melt in a vacuum or an inert atmosphere, and conduct directional solidification under an electromagnetic field; b. Cooling after directional solidification, separating silicon and alloy to obtain purified polysilicon. 2. the method for utilizing high-entropy alloy to purify polysilicon according to claim 1 is characterized in that, in step a, before high-entropy alloy is mixed with raw material silicon, high-entropy alloy is first pretreated, and the pretreatment method is: The high-entropy alloy is heated to melting under vacuum or in an inert atmosphere, and then cooled to room temperature with the furnace. 3 . The method for purifying polysilicon by using a high-entropy alloy according to claim 1 , wherein the melting point of the high-entropy alloy used is less than the melting point of silicon. 4 . 4 . The method for purifying polysilicon using a high-entropy alloy according to claim 2 , wherein the melting point of the high-entropy alloy used is less than the melting point of silicon. 5 . 5 . The method for purifying polysilicon by using a high-entropy alloy according to claim 1 , wherein in step a, the high-entropy alloy is composed of five elements. 6 . 6. the method that utilizes high-entropy alloy to purify polycrystalline silicon according to claim 5 is characterized in that, in step a, high-entropy alloy is made up of five elements of Co, Cr, Fe, Ni and Al, or high-entropy alloy is made of Co. , Cr, Fe, Ni, and Ti, or high-entropy alloys composed of Co, Cr, Fe, Ni, and Cu, or high-entropy alloys composed of Co, Cr, Fe, Ni, and Mn , or high-entropy alloys are composed of five elements, Al, Fe, Ni, Ti, and Cu. 7 . The method for purifying polysilicon by using high-entropy alloy according to claim 6 , wherein in step a, the high-entropy alloy is composed of five elements of Al, Fe, Ni, Ti and Cu. 8 . 8 . The method for purifying polysilicon by using a high-entropy alloy according to claim 7 , wherein in step a, the molecular formula of the high-entropy alloy is AlFeNiTiCu. 9 . 9. The method for purifying polysilicon using high-entropy alloy according to claim 1, wherein in step a: the purity of the raw material silicon is not less than 99 wt%. 10 . The method for purifying polycrystalline silicon by using a high-entropy alloy according to claim 1 , wherein in step a: the mass ratio of the high-entropy alloy to the raw silicon is 5:1 to 1:5. 11 . 11 . The method for purifying polysilicon by using a high-entropy alloy according to claim 5 , wherein, in step a: the mass ratio of the high-entropy alloy to the raw silicon is 5:1 to 1:5. 12 . 12 . The method for purifying polycrystalline silicon by using a high-entropy alloy according to claim 6 , wherein in step a: the mass ratio of the high-entropy alloy to the raw silicon is 5:1 to 1:5. 13 . 13 . The method for purifying polysilicon by using a high-entropy alloy according to claim 7 , wherein, in step a: the mass ratio of the high-entropy alloy to the raw silicon is 5:1 to 1:5. 14 . 14 . The method for purifying polycrystalline silicon by using a high-entropy alloy according to claim 8 , wherein in step a: the mass ratio of the high-entropy alloy to the raw silicon is 5:1 to 1:5. 15 . 15 . The method for purifying polysilicon by using a high-entropy alloy according to claim 10 , wherein, in step a: the mass ratio of the high-entropy alloy to the raw silicon is 1:2 to 2:1. 16 . 16 . The method for purifying polysilicon by using high-entropy alloy according to claim 15 , wherein, in step a: the mass ratio of high-entropy alloy to raw silicon is 1:1. 17 . 17 . The method for purifying polysilicon using high-entropy alloys according to claim 1 , wherein, in step a: the inert atmosphere is a nitrogen atmosphere or an argon atmosphere. 18 . 18 . The method for purifying polycrystalline silicon by high-entropy alloy according to claim 17 , wherein in step a: per gram of raw silicon, the flow rate of the inert gas blown in is 15-30 mL/min. 19 . 19. The method for purifying polycrystalline silicon by using high-entropy alloy according to claim 18, characterized in that, in step a: per gram of raw material silicon, the flow rate of the injected inert gas is 20 mL/min. 20 . The method for purifying polysilicon by high-entropy alloy according to claim 1 , wherein in step a: the heating temperature is 1250-1550° C. 21 . 21 . The method for purifying polysilicon using high-entropy alloys according to claim 1 , wherein in step b: the directional solidification speed is 1 mm/h to 10 mm/h. 22 .

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