CN112794332B - Method for removing boron impurities in metallurgical silicon by nitridation-purification - Google Patents
Method for removing boron impurities in metallurgical silicon by nitridation-purification Download PDFInfo
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Abstract
A method for removing boron impurities in metallurgical silicon by nitridation-purification belongs to the field of metallurgical materials. Hair brushAdding a nitriding agent into metallurgical-grade silicon melt, wherein the adding of the nitriding agent can convert boron impurities in the silicon melt into nitride particles, then applying electromagnetic force on the nitrided silicon melt to gather the nitride particles around the silicon melt, then forcibly cooling and separating the silicon melt and the nitride particles, and producing silicon nitride by using the separated polycrystalline silicon rich in the nitride particles; because the nitride particles and the silicon melt have obvious conductivity difference, the nitride particles can be enriched to the periphery of the melt under the action of electromagnetic force, thereby realizing the effective separation of boron impurities and the silicon melt; in addition, the polycrystalline silicon rich in nitride particles is comminuted, ammonium chloride is added and the flowability N is adjusted2Nitriding under atmosphere to obtain a silicon nitride product; and the high-efficiency utilization of resources is realized by using the polycrystalline silicon rich in nitride, and the technical economy is improved.
Description
Technical Field
The invention relates to the technical field of metallurgy and materials, in particular to a method for converting and purifying impurity boron in metallurgical silicon based on superfine nitride.
Background
China is a genuine large country for silicon production, but at present, the supply and demand of silicon materials in China face serious structural imbalance, and on one hand, the supply of the silicon materials at the middle and low ends is seriously excessive, and the price continuously declines; on the other hand, high quality silicon is not supplied sufficiently and highly depends on the inlet. Under the background, optimizing the product structure and improving the product quality are the necessary way for the silicon industry to realize sustainable development.
The solar grade polysilicon is one of high value-added silicon products with the most application prospect, has the purity of 5-7N, and is mainly applied to preparation of solar cell devices. The zinc reduction method was invented by dupont corporation in 1865, whereby the sequential curtain for the preparation of high purity polysilicon was opened up, followed by the sequential production of the silicon tetrachloride hydrogen reduction method, the trichlorosilane thermal decomposition method, the silane thermal decomposition method, and the modified siemens method, which became the mainstream preparation process of polysilicon. Since the 20 th century and the 70 th era, the photovoltaic industry has developed rapidly, so that the huge demand of the industry on solar grade polycrystalline silicon materials is stimulated, and the improved Siemens method cannot meet the large-scale production of polycrystalline silicon, so that a batch of novel high-purity polycrystalline silicon preparation technologies such as a metallurgy method, a metal reduction method, molten salt electrolysis and the like are developed by taking the large-scale production as a trigger. For solar grade polysilicon materials, the B impurity is a key impurity, and the resistivity of the silicon-based solar cell is too low due to the high content of the B impurity, so that the photoelectric conversion efficiency of the solar cell is influenced. However, the B impurity has similar properties to silicon and is the most difficult impurity to remove in the process of preparing solar grade polysilicon by the new technology, and for the removal of the B impurity, the prior art also faces the common problems of reducing the production cost and improving the product quality.
The main method for removing B impurities in silicon at present is a slagging-blowing refining method, wherein inert or inert-active mixed gas is introduced into a silicon-slag melt in the slagging refining process, and the melt is stirred by using the inert gas to promote element transmission and accelerate chemical reaction; the method for purifying the polycrystalline silicon has the advantages of high impurity removal efficiency, strong operability and low cost by utilizing the reaction of the impurities between the active gas and the silicon melt. Through retrieval, the invention has the name: a preparation process of low-boron-phosphorus high-purity silicon (application No. 201811088653.4, application date: 2018-09-18) discloses a preparation process of low-boron-phosphorus high-purity silicon, which comprises the following steps: preparing raw materials, removing metal impurities by acid washing, oxidizing, refining and removing phosphorus, removing boron by an improved heat exchange method, and reducing and purifying. The application adopts an acid washing mode to remove metal impurities in the industrial silicon, and then removes phosphorus and boron in the industrial silicon by an oxidation refining and improved heat exchange method, so that the phosphorus and the boron are oxidized to form volatile substances,although the purity of the silicon can reach more than 99.9 percent, H is introduced in the process of removing B2And water vapor and require a mortgage environment, resulting in a large loss of slag agent and silicon; meanwhile, a large amount of slag agents are used in the process, secondary pollution of silicon melt is inevitably caused, and the low-B polycrystalline silicon material is further obtained by refining methods such as slag-metal separation, acid pickling and the like, so that the cost is high, the flow is long, and the boron removal efficiency is low.
Disclosure of Invention
1. Technical problem to be solved by the invention
The invention aims to solve the problems of high cost, long flow, low efficiency and the like in removing boron impurities in silicon in the prior art, and provides a method for removing the boron impurities in metallurgical silicon by nitridation-purification.
2. Technical scheme
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
the invention relates to a method for removing boron impurities in metallurgical silicon by nitridation-purification, which comprises the steps of adding a nitriding agent into a metallurgical-grade silicon melt, applying electromagnetic force to the nitrided silicon melt to gather nitride particles around the silicon melt, forcibly cooling and separating the silicon melt and the nitride particles, and producing silicon nitride by using the separated polycrystalline silicon material rich in the nitride particles.
Preferably, the specific steps are as follows:
the first step is as follows: nitriding converting
Firstly, heating metallurgical-grade silicon to a molten state, and then blowing a nitridizing agent into a metallurgical-grade silicon melt to perform a nitriding reaction;
the second step is that: electromagnetic decontamination
Applying electromagnetic force to the nitrided melt obtained after the nitridation reaction in the step one to gather nitride particles around the silicon melt;
the third step: cooling and separating
Forcibly cooling the silicon melt obtained in the step two to obtain polycrystalline silicon rich in nitride particles around, and then mechanically separating the polycrystalline silicon rich in nitride particles around to respectively obtain polycrystalline silicon rich in nitride and polycrystalline silicon after boron removal;
the fourth step: silicon nitride preparation
And (4) crushing and nitriding the polycrystalline silicon rich in impurities obtained in the third step to obtain a silicon nitride product.
Preferably, the first step comprises the following specific steps: heating metallurgical-grade silicon to a temperature above a silicon melting point, preserving heat for 30-120 min to enable the metallurgical-grade silicon to be completely melted to form a metallurgical-grade silicon melt, and blowing a nitriding agent into the metallurgical-grade silicon melt by taking argon as a carrier gas to carry out a nitriding reaction.
Preferably, the third step comprises the following specific steps: and D, blowing nitrogen to the outer side of the silicon melt obtained in the step two for forced cooling, then closing the electromagnetic force to obtain polycrystalline silicon rich in nitride particles around, and then mechanically separating the polycrystalline silicon rich in nitride particles around to respectively obtain polycrystalline silicon rich in nitride particles and polycrystalline silicon after boron removal.
Preferably, the fourth step comprises the following specific steps: the polycrystalline silicon rich in nitride particles obtained in the third step is crushed, and ammonium chloride particles are added, and the fluidity N is high2And carrying out nitriding treatment in the atmosphere to obtain a silicon nitride product.
Preferably, the electromagnetic parameters of the electromagnetic purification are: current intensity is 10-50A, voltage: 200-550V, frequency: 50-100 kHz, power: 4 ~ 25kW, electromagnetism purifying time: 10 to 180 s.
Preferably, the nitriding agent is N2And/or NH3The nitrogen concentration of the nitriding agent is 0.1-10%, and the nitriding time is 5-180 s.
Preferably, the interface between the polycrystalline silicon mechanically separated from the nitrogen-rich particles and the polycrystalline silicon with low boron-containing impurities at the center in the fourth step is 5-15 mm from the surface to the inside of the polycrystalline silicon obtained in the third step.
Preferably, the purity of the metal powder M is higher than 99.9%, the metal powder M is one or more of Al, Ti and Si, and the particle size of the metal powder M is 1-30 μ M.
Preferably, the polysilicon rich in silicon nitride particles is crushed to a particle size range of 10-50 μm, the addition amount of ammonium chloride is 20-100% of the mass of the polysilicon rich in silicon nitride particles, and the particle size range of the ammonium chloride is 10-50 μm.
Preferably, the temperature range of the nitriding treatment is 600-1200 ℃, and the fluidity N is2The flow rate of the nitrogen source is 100-500 mL/min, and the nitriding time is 20-180 min.
3. Advantageous effects
Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:
(1) the invention relates to a method for removing boron impurities in metallurgical silicon by nitridation and purification, which comprises the steps of adding a nitriding agent into a metallurgical-grade silicon melt, wherein the addition of the nitriding agent can convert the boron impurities in the silicon melt into nitride particles, then applying electromagnetic force to the nitrided silicon melt to gather the nitride particles around the silicon melt, then carrying out forced cooling and separation on the silicon melt and the impurities, and producing silicon nitride by using the silicon material from which the nitride particles are separated; because the nitride particles and the silicon melt have obvious conductivity difference, the nitride particles can be enriched to the periphery of the melt under the action of electromagnetic force, thereby realizing the effective separation of boron impurities and the silicon melt;
(2) the invention relates to a method for removing boron impurities in metallurgical silicon by nitridation-purification, which comprises the steps of crushing polycrystalline silicon rich in silicon nitride particles, and adding ammonium chloride particles; flow rate N2Carrying out nitriding treatment in the atmosphere to obtain a silicon nitride product; the polycrystalline silicon rich in nitride particles is reasonably utilized and subjected to nitridation treatment, so that the high-efficiency utilization of resources can be realized, and the technical economy is improved;
(3) the invention relates to a method for removing boron impurities in metallurgical silicon by nitridation-purification, which is characterized in that electromagnetic force is applied to a nitrided melt, and nitrides are enriched around the nitrided melt under the action of the electromagnetic force, so that the separation of the nitrides and the silicon melt is realized; the electromagnetic purification only depends on the action of an electromagnetic external field to separate nitride particles from a melt, is a non-contact and clean refining technology, cannot introduce new media into the silicon melt to cause secondary pollution, and realizes efficient enrichment and removal of the particles; in addition, the electromagnetic purification process only needs to regulate and control parameters such as current intensity and the like to carry out efficient separation of the nitride particles and the silicon melt, and has the advantages of simple operation, low cost and high boron removal efficiency.
Drawings
FIG. 1 is a schematic diagram of a nitridation-purification method for removing impurities from metallurgical silicon according to the present invention.
Detailed Description
The detailed description and exemplary embodiments of the invention will be better understood when read in conjunction with the appended drawings, where the elements and features of the invention are identified by reference numerals.
Example 1
Referring to fig. 1, the method for removing boron impurities in metallurgical silicon by nitridation-purification according to the embodiment includes the following steps: adding a nitriding agent into a metallurgical-grade silicon melt, then applying electromagnetic force to the nitrided silicon melt to gather nitride particles around the silicon melt, then forcibly cooling and separating the silicon melt and the nitride particles, and producing silicon nitride by using the separated silicon material rich in nitride. The method comprises the following specific steps:
the first step is as follows: nitriding blowing
Firstly, heating metallurgical-grade silicon to be above a silicon melting point, and preserving heat for 30-120 min to enable the metallurgical-grade silicon to be completely melted to form a metallurgical-grade silicon melt, wherein the metallurgical-grade silicon is heated to 1650 ℃, the heat preservation time is 120min, the purity of the selected metallurgical-grade silicon is 95%, and the content of boron impurities is 500 ppm; then, blowing a nitriding agent into the metallurgical-grade silicon melt by taking argon as carrier gas to carry out nitriding reaction, wherein the nitriding agent is N2And/or NH3The nitrogen concentration of the nitriding agent is 0.1-10%, and the nitriding time is 5-180 s. The nitriding agent used in this example was N2The N concentration is 1%, and the nitriding time is 180 s;
it is noted that the addition of a nitriding agent to metallurgical grade silicon allows the boron impurity to be nitrided to BN, which is present in the silicon melt as solid particles, which are insoluble in the silicon melt and removable from the silicon melt; in addition, because Si is used as a substrate, the probability of reaction with the nitriding agent is far greater than that of reaction between B and N, and therefore, the silicon melt isIn which Si reacts with N to form Si3N4The number of particles is larger than that of BN particles, and Si is generated3N4The particles further adsorb unreacted boron impurities in the silicon melt and are nitrided to form Si3N4-BN composite particles and boron in the melt removed boron predominantly as Si3N4Mainly removing boron impurities by adsorption and nitridation.
It should be further noted that the nitriding agent used in this example is N2Which can be used not only for the formation of BN particles and Si3N4BN composite particles, and a carrier gas Ar in the form of bubbles in a silicon melt, the bubbles dispersed in the silicon melt facilitating the adsorption of BN particles, Si3N4Particles and Si3N4-BN composite particles promoting the removal of B impurities from the silicon melt;
the second step is that: electromagnetic decontamination
Applying electromagnetic force to the nitrided melt obtained after the nitridation reaction in the step one to gather impurities around the silicon melt; wherein, the electromagnetic parameters of the electromagnetic force are as follows: current intensity is 10-50A, voltage: 200-550V, frequency: 50-100 kHz, power: 4 ~ 25kW, electromagnetism purifying time: 10-180 s; specifically to the present embodiment, the current intensity 50A, the voltage: 200V, frequency: 50kHz, power: 10kW, purge time: 180 s;
notably, since impurities in silicon are converted into BN particles, Si3N4Particles and Si3N4BN composite particles, although the solid impurities can be gradually floated up and removed, the floating speed is slow and the efficiency is low, the production requirement cannot be met, but the obvious conductivity difference exists between solid phase particles and silicon melt at high temperature, and the solid phase particles which are not conductive or poor in conductivity are not or are not subjected to small electromagnetic force under the action of electromagnetic force; therefore, under the action of electromagnetic force, the Si generated in the nitriding converting stage3N4Particles, BN particles, Si3N4The BN composite particles will concentrate to the outside, bottom, top of the melt;
the third step: cooling and separating
And (4) spraying nitrogen agent to the outer side of the silicon melt obtained in the step two for forced cooling, and then closing the electromagnetic force to obtain the polycrystalline silicon rich in nitride particles around. In order to separate and remove the nitride particles, mechanically separating the polycrystalline silicon rich in the nitride particles around, and specifically, cutting and separating the polycrystalline silicon rich in the nitride particles from the surface to the inner part of the polycrystalline silicon 5-15 mm to respectively obtain the polycrystalline silicon rich in the nitride particles and the polycrystalline silicon after boron removal; the purpose of turning off the electromagnetic force after forced cooling is as follows: the outer side or the bottom and the top of the silicon melt are ensured to be solidified firstly, so that the nitride particles are ensured to be concentrated in the parts solidified firstly under the action of the electromagnetism;
the fourth step: silicon nitride preparation
Crushing the polycrystalline silicon rich in the nitride particles obtained in the third step to a particle size of 10-50 μm, wherein the crushed particle size is 10 μm; in addition, adding ammonium chloride particles, wherein the adding amount of the ammonium chloride particles is 20-100% of the mass of the polycrystalline silicon rich in impurities, and the particle size range of the ammonium chloride particles is 10-50 mu m; flow rate N2Nitriding under atmosphere to obtain a silicon nitride product, wherein the temperature range of nitriding is 600-1200 ℃, and the fluidity N is2The flow rate of (2) is 100-500 mL/min, the nitriding time is 20-180 min, and specifically in the embodiment, the nitriding temperature: 600 ℃ fluidity N2The flow rate of (2) is 100mL/min, the nitriding time: 180 min;
it is worth noting that in order to reasonably utilize the polysilicon rich in nitride particles, the nitride particles are subjected to nitridation treatment, so that the high-efficiency utilization of resources can be realized, and the technical economy is improved.
The boron impurity content of the finally obtained polysilicon is 20ppm, and the purity of the silicon nitride product reaches 99%.
Example 2
This example is substantially the same as example 1, except that: in the embodiment, metallurgical-grade silicon is heated to 1600 ℃, the heat preservation time is 60min, the purity of the metallurgical-grade silicon is 99%, and the content of boron impurities is 100 ppm. The nitriding agent adopted is NH3The N content was 5%, and the nitriding time was 120 seconds. Current intensity 40A in the second step, voltage: 500V, frequency: 80kHz, power: 20kW, purge time: 120 s. Book (I)Example in the fourth step, polycrystalline silicon rich in nitride particles was pulverized to 30 μm, ammonium chloride particles were added in an amount of 50% by mass of the polycrystalline silicon rich in nitride particles, and the nitriding temperature: fluidity N at 800 ℃2The flow rate of (2) is 200mL/min, the nitriding time: and (5) 90 min.
The boron impurity content of the finally obtained polysilicon is 5ppm, and the purity of the silicon nitride product reaches 99.6%.
It is noted that the nitriding agent used in this embodiment is NH3Of which and N2The difference as nitriding agent is NH3Besides boron as an impurity in silicon reacts to form BN, N can also be formed3H6B3Which is present in the silicon melt in the form of a gas phase and is not only easy to remove but also capable of adsorbing Si3N4Particles, BN particles, Si3N4And (4) floating up and removing the-BN composite particles together.
Example 3
This example is substantially the same as example 1, except that: in the embodiment, metallurgical-grade silicon is heated to 1500 ℃, the heat preservation time is 40min, the purity of the metallurgical-grade silicon is 99.5%, and the content of boron impurities is 50 ppm. The adopted nitriding agent is N2And NH3The N content was 8%, and the nitriding time was 100 seconds. Current intensity 35A in the second step, voltage: 300V, frequency: 70kHz, power: 10.5kW, purge time: for 60 s. In the fourth step of this example, polysilicon rich in nitride particles was pulverized to 15 μm, ammonium chloride particles were added in an amount of 100% by mass of the polysilicon rich in nitride particles, and the nitriding temperature: 900 ℃ fluidity N2The flow rate of (2) is 300mL/min, the nitriding time: and (5) 60 min.
The boron impurity content of the finally obtained polysilicon is 3ppm, and the purity of the silicon nitride product reaches 99.9%.
The invention has been described in detail hereinabove with reference to specific exemplary embodiments thereof. It will, however, be understood that various modifications and changes may be made without departing from the scope of the invention as defined in the appended claims. The detailed description and drawings are to be regarded as illustrative rather than restrictive, and any such modifications and variations are intended to be included within the scope of the present invention as described herein. Furthermore, the background is intended to be illustrative of the present development and significance of the technology and is not intended to limit the invention or the application and field of application of the invention.
Claims (8)
1. A method for removing boron impurities in metallurgical silicon by nitridation-purification is characterized in that a nitriding agent is added into a metallurgical-grade silicon melt, the nitriding agent has adsorption and nitridation effects on the boron impurities and can convert the boron impurities into nitrides, then electromagnetic force is applied to the nitrided silicon melt to gather nitride particles to the periphery of the silicon melt, then the silicon melt and the boron impurity particles are forcedly cooled and separated, and the polysilicon which is separated and is rich in the nitride particles is used for producing silicon nitride;
the method comprises the following specific steps:
the first step is as follows: nitriding blowing
Firstly, heating metallurgical-grade silicon to a molten state, and then blowing a nitridizing agent into a metallurgical-grade silicon melt to perform a nitriding reaction;
the second step is that: electromagnetic decontamination
Applying electromagnetic force to the nitrided melt obtained after the nitridation reaction in the step one to gather nitride particles around the silicon melt;
the third step: cooling and separating
Forcibly cooling the silicon melt obtained in the step two to obtain polycrystalline silicon rich in nitride particles around, and then mechanically separating the polycrystalline silicon rich in nitride particles around to respectively obtain polycrystalline silicon rich in nitride particles and polycrystalline silicon after boron removal;
the fourth step: silicon nitride preparation
Crushing the polycrystalline silicon rich in nitride particles obtained in the third step, and immediately carrying out nitridation treatment to obtain a silicon nitride product;
the mechanical separation interface is 5-15 mm from the surface to the inside of the polycrystalline silicon rich in nitride particles.
2. The method for removing boron impurities in metallurgical silicon by nitridation-purification according to claim 1, wherein the specific steps of the first step are as follows: firstly, heating metallurgical-grade silicon to be above a silicon melting point, preserving heat for 30-120 min to enable the metallurgical-grade silicon to be completely melted to form a metallurgical-grade silicon melt, and then blowing a nitriding agent into the metallurgical-grade silicon melt by taking argon as a carrier gas to carry out nitriding reaction.
3. The method for removing boron impurities in metallurgical silicon by nitridation-purification according to claim 1, wherein the third step comprises the following specific steps: and B, blowing nitrogen to the outer side of the silicon melt obtained in the step two for forced cooling, closing the electromagnetic force to obtain polycrystalline silicon rich in nitride particles around, and mechanically separating the polycrystalline silicon rich in the nitride particles around to respectively obtain polycrystalline silicon rich in the nitride particles and polycrystalline silicon subjected to boron removal.
4. The method for removing boron impurities in metallurgical silicon by nitridation-purification according to claim 1, wherein the fourth step comprises the following specific steps: the polycrystalline silicon rich in nitride particles obtained in the third step is crushed, and ammonium chloride particles are added, and the fluidity N is adjusted2And carrying out nitriding treatment under the atmosphere to obtain a silicon nitride product.
5. The method for removing boron impurities in metallurgical silicon by nitridation-purification according to claim 1 or 3, wherein the electromagnetic force has electromagnetic parameters as follows: current intensity is 10-50A, voltage: 200-550V, frequency: 50-100 kHz, power: 4 ~ 25kW, electromagnetism purifying time: 10 to 180 s.
6. A nitridation-purification method for removing boron impurities from metallurgical silicon according to claim 1 or 2, wherein: the nitriding agent is N2And/or NH3The nitrogen concentration of the nitriding agent is 0.1-10%, and the nitriding time is 5-180 s.
7. The nitridation-purification method for removing boron impurities in metallurgical silicon according to claim 4, wherein: the polycrystalline silicon rich in the nitride particles is crushed to a particle size range of 10-50 mu m, the adding amount of ammonium chloride is 20-100% of the mass of the polycrystalline silicon rich in the nitride particles, and the particle size range of the ammonium chloride particles is 10-50 mu m.
8. The method for removing boron impurities in metallurgical silicon by nitridation-purification according to claim 1 or 4, wherein: the temperature range of the nitriding treatment is 600-1200 ℃, and the fluidity N is2The flow rate of the nitrogen source is 100-500 mL/min, and the nitriding time is 20-180 min.
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