CN109970068B - Method for purifying polycrystalline silicon by using high-entropy alloy - Google Patents
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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
Technical Field
The invention relates to a method for purifying polycrystalline silicon by using high-entropy alloy, belonging to the field of high-crystalline silicon purification.
Background
Currently, solar grade polysilicon (6N) is primarily doped with semiconductor grade silicon (9N) produced by the modified siemens process. Although the average cost of polysilicon produced by the improved siemens process decreases from $ 70/kg in 2007 to $ 12/kg in 2017 as key technology breaks through and energy consumption decreases, the siemens process requires a doping process to ensure the best current transfer rate of the cell, which undoubtedly results in purity waste and increases the production cost.
In another method: the metallurgical method has the advantages of low energy consumption, environmental friendliness, sustainable production and the like, has huge market potential, and is becoming a hotspot of global research. The metallurgy method directly purifies industrial-grade silicon (2-3N) to solar-grade silicon (6N) by slagging refining, wet leaching, vacuum evaporation, directional solidification, electron beam and plasma refining and other impurity removal technologies. According to the east dream method of Ningxia east dream energy Co., Ltd, the process flow is characterized in that as shown in the attached figure 1, the method specifically comprises the following steps: in the step of slagging in the submerged arc furnace, the difference of the solubility of partial impurities in the mixed state of the metal silicon liquid and the slag liquid is utilized to realize physical separation at high temperature and remove specific impurities such as B, Al, Ca and the like; in the physical crushing step, the impurity at the grain boundary is physically separated from the silicon by utilizing the segregation principle of the impurity in the silicon (the fixed form of the impurity existing in the metallic silicon); in the hydrometallurgy step, impurities attached to the surface of a silicon material with small particle size and large surface area are subjected to acid leaching and separated out, and most of metal impurities are removed; in the electron beam zone melting step: the principle that a large amount of electrons are supplemented by electron beams and the characteristic of high-temperature gasification are utilized to realize deep phosphorus removal, iron removal and oxygen removal under high vacuum degree; and finally finishing the finished product. The main problems of the east dream method are: 1. the solubility is limited, and the boron removal effect is unstable; 2. multiple slag systems reduce efficiency.
Among the 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 has segregation coefficient (0.8) similar to that of silicon and low saturated vapor pressure (6.78 × 10 at 1823K, 10)-7Pa), are difficult to remove by the above-mentioned methods. Once the boron content in the solar-grade polysilicon exceeds 0.3ppmw, B-O defects are formed with interstitial oxygen and are compounded with electrons or holes to form a deep energy level, so that the service life of minority carriers is shortened, and the photoelectric conversion efficiency of the solar-grade polysilicon is influenced. In addition, the content of impurity boron in silicon is extremely low (10-30ppmw), the activity is very low, and the removal difficulty is increased.
At present, researchers at home and abroad mainly adopt four methods for refining and removing boron, namely slag refining, alloy refining, blowing refining and plasma refining, and a vacuum plasma method is used for removing B (OH) O formed after ionization of a high-temperature plasma gun, but the vacuum plasma method cannot be produced in mass due to the defects of expensive equipment, complex operation, low yield, easy explosion and the like. The blowing refining is to refine the silicon liquid by adopting a ventilation mode, and although C, O, B and the like have better removal effect, the silicon liquid is not easy to fully contact with impurities, so that the impurity removal effect is poor; the slagging process is to melt silicon, add basic oxide and acidic oxide, and absorb impurities in silicon liquid into slag. The traditional alloy method is proposed in 2005 by professor Jichuan of Tokyo university to remove boron impurities in silicon by using a Si-Al alloy directional solidification method. Later researchers used alloys such as Si-Al-Sn, Si-Sn, Cu-Si, etc. to remove boron impurities. However, the conventional alloying methods such as silicon aluminum and silicon tin have 2 problems: 1. if the directional solidification is carried out in the common resistance furnace instead of the electromagnetic induction furnace, the silicon phase and the alloy phase can not be separated; in the Si — Al alloy method, it can be seen from the article of the professor of the jichuang key, which was the founder of the alloy method, that only the alloy can be formed by resistance heating, and only under the precondition of induction heating, the alloy phase can be separated from the silicon phase due to the electromagnetic stirring. Si-Sn works in the same way. According to our experiments and papers published by the Chinese academy of technology, a separate approach is to digest the alloy phase with hydrochloric acid, leaving a pure silicon phase. The method is the most effective separation method at present, so the alloy can be used only once and cannot be used repeatedly, and the method is also the bottleneck for restricting the application. 2. In order to effectively remove boron impurities, the ratio of aluminum to tin is required to be large, so that silicon-aluminum and silicon-tin alloy with the mass ratio of more than 70% can be formed after directional solidification, only a small part of pure silicon is always formed, and the silicon yield is low.
The requirement of solar grade silicon on the content of impurity boron is difficult to achieve by singly applying a certain method, although researchers at home and abroad try to make certain progress on coupling methods such as a slagging-blowing method, a slagging-alloying method, a slagging-pickling method and the like, the problems of high energy consumption, poor stability, high cost and the like are solved, and the B removing effect obtained by different researchers is greatly different, so that the difficulty of reducing the content of B in silicon to the standard (less than 0.3ppmw) of polycrystalline silicon for solar batteries is certain. In summary, in order to overcome the limitations of the above four methods, a method is urgently needed, which limits the above four methods, improves the partition ratio of boron in the alloy phase and the silicon phase, simplifies the steps, and achieves the purpose of deep, effective and low-cost boron removal.
On the other hand, since 2004, professors in the root of the Chinese patent application teach "high entropy alloy", more and more researchers found that when an alloy consisting of 5 or more than 5 kinds of metal or nonmetal elements with equal composition is a new type of solid solution alloy, it has four characteristics: (1) the high entropy effect forms a simple solid solution without intermediate compounds; (2) a slow diffusion effect; (3) severe lattice distortion; (4) cocktail effect. The developed high-entropy alloy shows high strong hardness, excellent wear resistance and corrosion resistance, and good high-temperature stability. Has received wide attention from scholars in the field of material science and engineering.
In the aspect of the preparation process of the high-entropy alloy, the commonly used method for preparing the high-entropy alloy block comprises the following steps: vacuum melting, spark plasma sintering, powder metallurgy, mechanical alloying, laser 3D printing, directional solidification and the like. The periodic table positions of the high-entropy alloy elements can be roughly divided into two types: one is a low-melting-point alloy system consisting of CoCrFeNi- (A1, Ti, Cu and Mn) metal elements; the other is a high-melting-point and high-entropy alloy system composed of high-melting-point metal elements such as Ti, Nb, Ta, Mo and W. At present, no report of purifying polycrystalline silicon by using high-entropy alloy exists.
Disclosure of Invention
Aiming at the defects, the technical problem solved by the invention is to provide a method for purifying polycrystalline silicon by using high-entropy alloy. Boron impurities in silicon can be reduced in a short treatment time by a simple method.
The invention utilizes the body-centered cubic structure of the high-entropy alloy to absorb impurities such as boron and the like in silicon which are difficult to remove; and (3) separating the high-entropy alloy phase from the silicon phase by using a vacuum electromagnetic induction furnace and a directional solidification device. The schematic diagram of the directional solidification induction refining of the high-entropy alloy and the schematic diagram of the alloy solidification refining are shown in the attached figure 2 in the specification. Wherein, the high-entropy alloy refers to an alloy formed by five or more equal or approximately equal metals.
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.
The polycrystalline silicon can be industrial grade silicon or polycrystalline silicon.
In the step a, the high-entropy alloy and the raw material silicon can be selectively mixed in a crucible, and preferably, the crucible is made of graphite or corundum. And then placing the crucible in a heating device for heating, preferably, the heating device is a medium-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 the step a, the high-entropy alloy is pretreated before being mixed with the raw material silicon, and the pretreatment method comprises the following steps: heating the high-entropy alloy to be molten in vacuum or inert atmosphere, and then cooling the high-entropy alloy to room temperature along with the furnace.
High-melting-point noble metals such as Ti, Nb, Ta, Mo, W and the like are generally used for the high-entropy alloy due to high melting point. In order to save cost, the high-entropy alloy used by the invention is a low-melting-point high-entropy alloy, and preferably, the melting point of the high-entropy alloy is less than or equal to that of silicon. The melting point of silicon is approximately 1420 ℃.
Further, in the step a, the high-entropy alloy consists of 5 elements; in order to further reduce the content of B in the polycrystalline silicon, preferably, the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Al, or the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Ti, or the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Cu, or the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Mn, or the high-entropy alloy consists of five elements of Al, Fe, Ni, Ti and Cu; further preferably, the entropy alloy consists of five elements of Al, Fe, Ni, Ti and Cu;
more preferably, the molecular formula of the high-entropy alloy is AlFeNiTiCu, CoCrFeNiAl and CoCrFeNi0.5Cu1.5CoCrFeNiMn; 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 99 wt%.
The adding amount of the high-entropy alloy influences the removal efficiency of impurities, and further in the step b: the mass ratio of the high-entropy alloy to the raw material silicon is 5: 1-1: 5; the mass ratio of the high-entropy alloy to the raw material silicon is preferably 1: 2-2: 1, and the mass ratio of the high-entropy alloy to the raw material silicon is more preferably 1: 1.
Further, in step a: the inert gas is argon or nitrogen.
The gas flow rate of the invention is related to the weight of the raw material silicon, and further, in the step a: the flow rate of the blown inert gas is 15-30 mL/min per gram of raw material silicon; preferably, the flow rate of the inert gas blown in is 20mL/min per gram of the raw material silicon.
The invention can be realized by melting the raw material silicon at a temperature, and in order to better purify the silicon and ensure the chemical reaction rate and good fluidity of the slag, the invention further comprises the following steps: the heating temperature is 1250-1550 ℃.
The directional solidification rate of the present invention is theoretically as slow as possible, but too slow increases the production time, too fast does not cause phase separation, and silicon and alloy are not separated. Therefore, it is preferred that in step b: the directional solidification speed is 1 mm/h-10 mm/h.
Further, in the step b, the cooling mode is closed cooling or normalized cooling.
The invention has the beneficial effects that:
1. the invention utilizes the high-entropy alloy to purify the polysilicon, and innovatively provides a method for removing boron impurities in industrial silicon by utilizing a novel high-entropy alloy material in the purification process of the polysilicon. By utilizing the characteristics of solid solution structure, diffusion delay and the like of the high-entropy alloy, crystalline silicon is preferentially separated out in high-temperature melting and directional solidification, and boron as an impurity is enriched in a high-entropy alloy phase according to the segregation principle, so that the aim of greatly reducing boron impurities in the crystalline silicon is fulfilled. The separation principle of the high-entropy alloy purified polysilicon is that the Me-B interaction coefficient of the traditional alloy method is larger than that of Si-B, so that B can move from silicon to the alloy, and an FCC simple face-centered cubic structure solid solution can be formed on the structure, so that B elements can be easily transferred to the high-entropy alloy phase in dynamics.
2. Compared with the traditional alloy method, the alloy is firstly formed among the alloy elements due to the high entropy characteristic and does not react with silicon, so that the silicon raw material is saved; the conventional alloying method reacts with silicon, resulting in a large loss of silicon raw material.
3. The invention combines the advanced material high-entropy alloy and the directional solidification method under the electromagnetic field, breaks through the limit of a single method for removing impurity boron, improves the wear-resisting property of the alloy while realizing boron removal in silicon, and provides a new idea for the boron removal link of the technology for preparing solar grade silicon at low cost.
4. The traditional alloy method reduces the reuse efficiency due to the increase of the impurity content of B after the test, and the high-entropy alloy can improve the wear resistance due to the B element, so that the high-entropy alloy can be applied to the industries of welding, bearings, wear-resistant coatings, golf club heads and the like.
5. The method has the advantages of simple steps, high boron removal efficiency and low cost.
6. The boron removal rate of the polysilicon purified by the method is over 90 percent, and the yield of the polysilicon is over 80 percent; when the high-entropy alloy AlFeNiTiCu is adopted for treatment, the boron removal rate is 99.4%, the yield of the polycrystalline silicon is 82%, the content of B in the obtained polycrystalline silicon is 0.3ppmw, and the requirement of solar-grade silicon is met.
Drawings
FIG. 1 is a process flow of the "east Meng method";
in FIG. 2, a is a schematic view of the directional solidification induction refining of the present invention; b is a principle diagram of alloy solidification and refining, and small black dots in the diagram B represent B impurities.
Detailed Description
Aiming at the defects, the technical problem solved by the invention is to provide a method for purifying polycrystalline silicon by using high-entropy alloy. Boron impurities in silicon can be reduced in a short treatment time by a simple method.
The invention utilizes the body-centered cubic structure of the high-entropy alloy to absorb impurities such as boron and the like in silicon which are difficult to remove; and (3) separating the high-entropy alloy phase from the silicon phase by using a vacuum electromagnetic induction furnace and a directional solidification device. The schematic diagram of the directional solidification induction refining of the high-entropy alloy and the schematic diagram of the alloy solidification refining are shown in the attached figure 2 in the specification. Wherein, the high-entropy alloy refers to an alloy formed by five or more equal or approximately equal metals.
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.
The polycrystalline silicon can be industrial silicon or polycrystalline silicon, and the content of B in the raw material silicon is 10-50 ppmw; preferably, the content of B in the raw material silicon is 30-50 ppmw.
In the step a, the high-entropy alloy and the raw material silicon can be selectively mixed in a crucible, and preferably, the crucible is made of graphite or corundum. And then placing the crucible in a heating device for heating, preferably, the heating device is a medium-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 the step a, the high-entropy alloy is pretreated before being mixed with the raw material silicon, and the pretreatment method comprises the following steps: heating the high-entropy alloy to be molten in vacuum or inert atmosphere, and then cooling the high-entropy alloy to room temperature along with the furnace.
High-melting-point noble metals such as Ti, Nb, Ta, Mo, W and the like are generally used for the high-entropy alloy due to high melting point. In order to save cost, the high-entropy alloy used by the invention is a low-melting-point high-entropy alloy, and preferably, the melting point of the high-entropy alloy is less than or equal to that of silicon. The melting point of silicon is approximately 1420 ℃.
Further, in the step a, the high-entropy alloy consists of 5 elements; in order to further reduce the content of B in the polycrystalline silicon, preferably, the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Al, or the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Ti, or the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Cu, or the high-entropy alloy consists of five elements of Co, Cr, Fe, Ni and Mn, or the high-entropy alloy consists of five elements of Al, Fe, Ni, Ti and Cu; further preferably, the entropy alloy consists of five elements of Al, Fe, Ni, Ti and Cu;
more preferably, the molecular formula of the high-entropy alloy is AlFeNiTiCu, CoCrFeNiAl and CoCrFeNi0.5Cu1.5CoCrFeNiMn; 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 99 wt%.
The adding amount of the high-entropy alloy influences the removal efficiency of impurities, and further in the step b: the mass ratio of the high-entropy alloy to the raw material silicon is 5: 1-1: 5; the mass ratio of the high-entropy alloy to the raw material silicon is preferably 1: 2-2: 1, and the mass ratio of the high-entropy alloy to the raw material silicon is more preferably 1: 1.
Further, in step a: the inert gas is argon or nitrogen.
The gas flow rate of the invention is related to the weight of the raw material silicon, and further, in the step a: the flow rate of the blown inert gas is 15-30 mL/min per gram of raw material silicon; preferably, the flow rate of the inert gas blown in is 20mL/min per gram of the raw material silicon.
The invention can be realized by melting the raw material silicon at a temperature, and in order to better purify the silicon and ensure the chemical reaction rate and good fluidity of the slag, the invention further comprises the following steps: the heating temperature is 1250-1550 ℃.
The directional solidification rate of the present invention is theoretically as slow as possible, but too slow increases the production time, too fast does not cause phase separation, and silicon and alloy are not separated. Therefore, it is preferred that in step b: the directional solidification speed is 1 mm/h-10 mm/h.
Further, in the step b, the cooling mode is closed cooling or normalized cooling.
Wherein, after directional solidification and cooling, the obtained product has an obvious interface of an alloy phase and a silicon phase, and the silicon and the alloy are separated by cutting and separating with refined steel stones according to the interface.
The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.
Wherein the yield calculation formula in the following examples and comparative examples is: yield is the mass of pure silicon obtained after cutting/mass of initial silicon.
Example 1
1) 5g of raw material industrial grade silicon with the impurity boron content of 50ppmw is weighed, and 5g of high-purity alloy powder is weighed according to the AlFeNiTiCu proportion with the same molar ratio.
2) Under argon atmosphere, AlFeNiTiCu is pre-melted at 1250 ℃ and cooled to an ingot.
3) Mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, putting the graphite crucible into an electromagnetic induction heating furnace, and melting the mixture at 1250 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 1mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) And (3) cutting and separating the silicon and the alloy by using refined steel stones, wherein the yield of the polycrystalline silicon is 82.1%, sampling and digesting for ICP detection, the boron content is reduced to 0.3ppmw, and the boron content of the alloy phase is increased to 48.7 ppmw.
Example 2
1) 10g of raw material industrial grade silicon with the impurity boron content of 50ppmw is weighed, and 5g of high-purity alloy powder is weighed according to the AlFeNiTiCu proportion with the same molar ratio.
2) Under argon atmosphere, AlFeNiTiCu is pre-melted at 1300 ℃ and cooled to an ingot.
3) And mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, and putting the graphite crucible into an electromagnetic induction heating furnace to melt at 1300 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 10mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) And (3) cutting and separating the silicon and the alloy by using refined steel stones, wherein the yield of the polycrystalline silicon is 84.7%, sampling and digesting for ICP detection, the boron content is reduced to 0.9ppmw, and the boron content of the alloy phase is increased to 48.9 ppmw.
Example 3
1) 5g of raw material industrial grade silicon with the impurity boron content of 10ppmw is weighed, and 5g of high-purity alloy powder is weighed according to the AlFeNiTiCu proportion with the same molar ratio.
2) Under argon atmosphere, AlFeNiTiCu is pre-melted at 1250 ℃ and cooled to an ingot.
3) Mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, putting the graphite crucible into an electromagnetic induction heating furnace, and melting the mixture at 1250 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 1mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) And (3) cutting and separating the silicon and the alloy by using refined steel stones, wherein the yield of the polycrystalline silicon is 80.3%, sampling and digesting for ICP detection, the boron content is reduced to 0.28ppmw, and the boron content of the alloy phase is increased to 0.71 ppmw.
Example 4
5g of raw material industrial grade silicon with the impurity boron content of 50ppmw is weighed, 1g of high-purity alloy powder is weighed according to the AlFeNiTiCu proportion with the same molar ratio, and the rest of the operation is the same as that in example 1. The yield of the polycrystalline silicon prepared in the embodiment is 94.1%, digestion is carried out after sampling, ICP detection is carried out, the boron content is reduced to 4.5ppmw, and the boron content of the alloy phase is increased to 45.6 ppmw.
Example 5
5g of raw material industrial grade silicon with the impurity boron content of 50ppmw is weighed, 25g of high-purity alloy powder is weighed according to the AlFeNiTiCu proportion with the same molar ratio, and the rest of the operation is the same as that in the embodiment 1. The yield of the polycrystalline silicon prepared in the embodiment is 82.6%, digestion is carried out after sampling, ICP detection is carried out, the boron content is reduced to 0.28ppmw, and the boron content of the alloy phase is increased to 48.6 ppmw.
Example 6
1) 5g of raw material silicon with the boron content of 50ppmw is weighed, and 5g of metal powder is weighed according to CoCrFeNiAl with the same molar ratio.
2) Under argon atmosphere, CoCrFeNiAl is pre-melted at 1450 ℃ and cooled to an ingot.
3) Mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, putting the graphite crucible into an electromagnetic induction heating furnace, and melting the mixture at 1450 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 5mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) The silicon and the alloy are cut and separated by fine steel stones, the yield of the polycrystalline silicon is 90.2%, digestion is carried out after sampling for ICP detection, the boron content is reduced to 2.7ppmw, and the boron content of the alloy phase is increased to 47.0 ppmw.
Example 7
1) 5g of raw material silicon with the boron content of 50ppmw is weighed, and 10g of metal powder is weighed according to CoCrFeNiAl with the same molar ratio.
2) Under argon atmosphere, CoCrFeNiAl is pre-melted at 1500 ℃ and cooled to an ingot.
3) And mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, and putting the graphite crucible into an electromagnetic induction heating furnace to melt at 1500 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 1mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) The silicon and the alloy are cut and separated by fine steel stones, the yield of the polycrystalline silicon is 88.3%, digestion is carried out after sampling for ICP detection, the boron content is reduced to 1.4ppmw, and the boron content of the alloy phase is increased to 48.2 ppmw.
Example 8
1) Weighing 5g of raw material silicon with the boron content of 50ppmw, and obtaining CoCrFeNi with the same molar ratio0.5Cu1.5The metal powder was weighed to give a total of 5 g.
2) Under argon atmosphere, CoCrFeNi0.5Cu1.5Pre-melting at 1500 ℃, and cooling to an ingot.
3) And mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, and putting the graphite crucible into an electromagnetic induction heating furnace to melt at 1500 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 2mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) And (3) cutting and separating the silicon and the alloy by using refined steel stones, wherein the yield of the polycrystalline silicon is 91.7%, sampling and digesting for ICP detection, the boron content is reduced to 1.8ppmw, and the boron content of the alloy phase is increased to 47.5 ppmw.
Example 9
1) Weighing boronCoCrFeNi in an amount of 5g of raw silicon in an equivalent molar ratio of 50ppmw0.5Cu1.5The metal powder was weighed to give a total of 10 g.
2) Under argon atmosphere, CoCrFeNi0.5Cu1.5Pre-melting at 1500 ℃, and cooling to an ingot.
3) And mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, and putting the graphite crucible into an electromagnetic induction heating furnace to melt at 1500 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 8mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) The silicon and the alloy are cut and separated by fine steel stones, the yield of the polycrystalline silicon is 91.0%, digestion is carried out after sampling for ICP detection, the boron content is reduced to 2.9ppmw, and the boron content of the alloy phase is increased to 46.5 ppmw.
Example 10
1) 5g of raw material silicon with the boron content of 50ppmw is weighed, and 5g of metal powder is weighed according to CoCrFeNiMn with the same molar ratio.
2) Under argon atmosphere, CoCrFeNiMn is pre-melted at 1550 ℃ and cooled to an ingot.
3) And mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, putting the graphite crucible into an electromagnetic induction heating furnace, and melting the mixture at 1550 ℃ under the argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 10mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) And (3) carrying out fine steel stone cutting separation on the silicon and the alloy, sampling, digesting and carrying out ICP detection, wherein the boron content is reduced to 4.8ppmw, and the boron content of the alloy phase is increased to 44.5 ppmw.
Example 11
1) 5g of raw material silicon with the boron content of 50ppmw is weighed, and 10g of metal powder is weighed according to CoCrFeNiMn with the same molar ratio.
2) Under argon atmosphere, CoCrFeNiMn is pre-melted at 1550 ℃ and cooled to an ingot.
3) And mixing the pre-melted alloy and industrial silicon, putting the mixture into a graphite crucible, putting the graphite crucible into an electromagnetic induction heating furnace, and melting the mixture at 1550 ℃ under the argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 5mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) The silicon and the alloy are cut and separated by fine steel stones, the yield of the polycrystalline silicon is 89.4%, digestion is carried out after sampling for ICP detection, the boron content is reduced to 3.1ppmw, and the boron content of the alloy phase is increased to 46.5 ppmw.
Comparative example 1
1) 5g of raw material industrial grade silicon with the impurity boron content of 50ppmw is weighed, and 5g of high-purity Sn powder is weighed.
2) Under argon atmosphere, Sn powder is pre-melted at 1250 ℃ and cooled to an ingot.
3) And mixing the pre-melted Sn and industrial silicon, putting the mixture into a graphite crucible, and putting the graphite crucible into an electromagnetic induction heating furnace to melt at 1250 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 1mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) The silicon and the alloy are cut and separated by fine steel stones, the yield of the polycrystalline silicon is 37.1%, digestion is carried out after sampling for ICP detection, the boron content is reduced to 3.62ppmw, and the boron content of the alloy phase is increased to 46.2 ppmw.
Comparative example 2
1) 5g of raw material industrial grade silicon with the impurity boron content of 50ppmw is weighed, and 5g of high-purity Al powder is weighed.
2) Under argon atmosphere, Al powder is pre-melted at 1250 ℃ and cooled to an ingot.
3) Mixing the pre-melted Al and industrial silicon, putting the mixture into a graphite crucible, and putting the graphite crucible into an electromagnetic induction heating furnace to melt at 1250 ℃ in an argon atmosphere.
4) After complete melting, the mixture is directionally solidified in an induction furnace, the pulling-down speed is 1mm/h, silicon is firstly separated out, an alloy phase is then separated out, and normalizing cooling is carried out.
5) And (3) cutting and separating the silicon and the alloy by using refined steel stones, wherein the yield of the polycrystalline silicon is 35.7%, sampling and digesting for ICP detection, the boron content is reduced to 2.63ppmw, and the boron content of the alloy phase is increased to 47.2 ppmw.
Claims (21)
1. The method for purifying the polycrystalline silicon by using the high-entropy alloy is characterized by comprising the following steps of:
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.
2. The method for purifying polycrystalline silicon by using the high-entropy alloy as claimed in claim 1, wherein in the step a, the high-entropy alloy is pretreated before being mixed with the raw material silicon, and the pretreatment method comprises the following steps: heating the high-entropy alloy to be molten in vacuum or inert atmosphere, and then cooling the high-entropy alloy to room temperature along with the furnace.
3. A method of purifying polysilicon using a high entropy alloy as claimed in claim 1, wherein the melting point of the high entropy alloy used is not more than the melting point of silicon.
4. A method of purifying polysilicon using a high entropy alloy as claimed in claim 2, wherein the melting point of the high entropy alloy used is not more than the melting point of silicon.
5. A method for purifying polysilicon by using a high-entropy alloy as claimed in any one of claims 1 to 4, wherein in the step a, the high-entropy alloy is composed of 5 elements.
6. A method for purifying polysilicon by using high-entropy alloy as claimed in claim 5, wherein in the step a, 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 of Co, Cr, Fe, Ni and Ti, or the high-entropy alloy is composed of five elements of Co, Cr, Fe, Ni and Cu, or the high-entropy alloy is composed of five elements of Co, Cr, Fe, Ni and Mn, or the high-entropy alloy is composed of five elements of Al, Fe, Ni, Ti and Cu.
7. A method for purifying polysilicon by using high-entropy alloy as claimed in claim 6, wherein in the step a, the high-entropy alloy is composed of five elements of Al, Fe, Ni, Ti and Cu.
8. The method for purifying polysilicon by using high-entropy alloy as claimed in claim 7, wherein in the step a, the molecular formula of the high-entropy alloy is AlFeNiTiCu.
9. The method for purifying polycrystalline silicon by using the high-entropy alloy as claimed in claim 1, wherein in the step a: the purity of the raw material silicon is not less than 99 wt%.
10. A method for purifying polycrystalline silicon by using a high-entropy alloy according to any one of claims 1 to 4, wherein in the step a: the mass ratio of the high-entropy alloy to the raw material silicon is 5: 1-1: 5.
11. A method for purifying polysilicon by using high-entropy alloy as claimed in claim 5, wherein in the step a: the mass ratio of the high-entropy alloy to the raw material silicon is 5: 1-1: 5.
12. The method for purifying polycrystalline silicon by using the high-entropy alloy as claimed in claim 6, wherein in the step a: the mass ratio of the high-entropy alloy to the raw material silicon is 5: 1-1: 5.
13. The method for purifying polycrystalline silicon by using the high-entropy alloy as claimed in claim 7, wherein in the step a: the mass ratio of the high-entropy alloy to the raw material silicon is 5: 1-1: 5.
14. The method for purifying polycrystalline silicon by using the high-entropy alloy as claimed in claim 8, wherein in the step a: the mass ratio of the high-entropy alloy to the raw material silicon is 5: 1-1: 5.
15. A method for purifying polysilicon using high entropy alloy as claimed in claim 10, wherein in step a: the mass ratio of the high-entropy alloy to the raw material silicon is 1: 2-2: 1.
16. A method for purifying polysilicon using high entropy alloy as claimed in claim 15, wherein in step a: the mass ratio of the high-entropy alloy to the raw material silicon is 1: 1.
17. The method for purifying polycrystalline silicon by using the high-entropy alloy as claimed in claim 1, wherein in the step a: the inert atmosphere is nitrogen atmosphere or argon atmosphere.
18. A method for purifying polysilicon using high entropy alloy as claimed in claim 17, wherein in step a: the flow rate of the blown inert gas is 15-30 mL/min per gram of raw material silicon.
19. A method for purifying polysilicon using high entropy alloy as claimed in claim 18, wherein in step a: the flow rate of the inert gas blown in per gram of the raw material silicon was 20 mL/min.
20. A method for purifying polycrystalline silicon by using a high-entropy alloy according to any one of claims 1 to 4, wherein in the step a: the heating temperature is 1250-1550 ℃.
21. A method for purifying polycrystalline silicon by using a high-entropy alloy according to any one of claims 1 to 4, wherein in the step b: the directional solidification speed is 1 mm/h-10 mm/h.
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