CN112794332B - Method for removing boron impurities in metallurgical silicon by nitridation-purification - Google Patents

Abstract

A method for nitriding-purifying removal of boron impurities in metallurgical silicon belongs to the field of metallurgical materials. In the present invention, a nitriding agent is added to the metallurgical grade silicon melt. The addition of the nitriding agent can convert boron impurities in the silicon melt into nitride particles, and then electromagnetic force is applied to the nitrided silicon melt to convert the nitride particles. Aggregate around the silicon melt, then force the silicon melt and the nitride particles to cool and separate, and use the above-separated polysilicon rich in nitride particles to produce silicon nitride; due to the gap between the nitride particles and the silicon melt There is a significant difference in conductivity, so under the action of electromagnetic force, nitride particles will be enriched around the melt, so as to achieve effective separation of boron impurities and silicon melt; in addition, the polysilicon rich in nitride particles is pulverized, The silicon nitride product is obtained by adding ammonium chloride and nitriding in a fluid N ₂ atmosphere; using the polysilicon rich in nitrides, the efficient utilization of resources is realized and the technical economy is improved.

Description

A method for nitriding-purifying removal of boron impurities in metallurgical silicon

technical field

The invention relates to the technical fields of metallurgy and materials, and more particularly, to a method for converting and purifying impurity boron in metallurgical silicon based on ultrafine nitrides.

Background technique

my country is a veritable silicon producer, but at present, the domestic supply and demand of silicon materials is facing a serious structural imbalance. import. In this context, optimizing product structure and improving product quality is the only way for the silicon industry to achieve sustainable development.

Solar-grade polysilicon is one of the most promising high-value-added silicon products, with a purity of 5-7N, and is mainly used in the preparation of solar cell devices. In 1865, the DuPont Company of the United States invented the zinc reduction method, which opened the prelude to the preparation of high-purity polysilicon. Among them, the modified Siemens method has become the mainstream preparation process of polysilicon. Since the 1970s, the photovoltaic industry has developed rapidly, which has stimulated the industry's huge demand for solar-grade polysilicon materials, and the improved Siemens method has been unable to meet the large-scale production of polysilicon. A batch of new high-purity polysilicon preparation technologies such as metal reduction method and molten salt electrolysis. For solar-grade polysilicon materials, B impurity is a key impurity, and if its content is too high, the resistivity of silicon-based solar cells will be too low, thereby affecting the photoelectric conversion efficiency of solar cells. However, B impurities are similar in properties to silicon, and are the most difficult impurities to remove in the process of preparing solar-grade polysilicon by new technologies. For the removal of B impurities, the existing technologies are still faced with the commonality of "reducing production costs" and "improving product quality" question.

At present, the main method for removing B impurities in silicon is slagging-air refining method. In the process of slagging and refining, inert or inert-active mixed gas is introduced into the silicon-slag melt, and the melt is stirred with inert gas to promote element transfer. , speed up the chemical reaction; use the reactive gas to react with the impurities between the silicon melt, which is a polysilicon purification method with high impurity removal efficiency, strong operability and low cost. After searching, the name of the invention and creation is: a preparation process of high-purity silicon with low boron and phosphorus (application number: 201811088653.4, application date: 2018-09-18), which discloses the preparation of high-purity silicon with low boron and phosphorus The process includes the following steps: preparing raw materials, removing metal impurities by acid washing, removing phosphorus by oxidative refining, removing boron by an improved heat exchange method, and reducing and purifying. This application uses acid washing to remove metal impurities in industrial silicon, and then removes phosphorus and boron in industrial silicon by oxidative refining and improved heat exchange, so that both phosphorus and boron are oxidized to form volatile substances. The purity of silicon reaches more than 99.9%, but in the process of removing B, _H2 and water vapor are introduced and the environment needs to be mortgaged, resulting in a large loss of slag agent and silicon; at the same time, the above process uses a large amount of slag agent, which inevitably causes Secondary pollution of silicon melt requires further refining methods such as slag gold separation and pickling to obtain low-B polysilicon materials, so the cost is high, the process is long, and the boron removal efficiency is low.

SUMMARY OF THE INVENTION

1. The technical problem to be solved by the invention

The purpose of the present invention is to solve the problems of high cost, long process and low efficiency in removing boron impurities in silicon in the prior art, and provide a method for removing boron impurities in metallurgical silicon by nitriding-purification. A nitriding agent is added to the nitriding agent, which reacts with impurities to form nitrides, and then uses electromagnetic purification means to efficiently remove the nitrides, so as to achieve the purpose of boron removal.

2. Technical solutions

In order to achieve the above object, the technical scheme provided by the invention is:

According to a method for nitriding-purifying and removing boron impurities in metallurgical silicon of the present invention, a nitriding agent is added to a metallurgical grade silicon melt, and then an electromagnetic force is applied to the silicon melt after nitridation to transfer the nitride particles to the silicon melt. Aggregate around, and then force the silicon melt and nitride particles to cool and separate, and use the separated polysilicon material rich in nitride particles to produce silicon nitride.

Preferably, the specific steps are as follows:

Step 1: Nitriding blowing

First, the metallurgical grade silicon is heated to a molten state, and then the nitriding agent is blown into the metallurgical grade silicon melt for nitriding reaction;

Step 2: Electromagnetic Purification

applying electromagnetic force to the nitrided melt obtained after the nitridation reaction in step 1, to gather the nitride particles around the silicon melt;

The third step: cooling separation

The silicon melt obtained in step 2 is forcibly cooled to obtain surrounding polysilicon rich in nitride particles, and then the above-mentioned surrounding polysilicon rich in nitride particles is mechanically separated to obtain nitride-rich polysilicon and boron-removed polysilicon respectively. polysilicon;

Step 4: Silicon Nitride Preparation

The impurity-rich polysilicon obtained in the third step is pulverized and nitrided to obtain a silicon nitride product.

Preferably, the specific steps of the first step are: firstly heating the metallurgical grade silicon to above the melting point of silicon and holding the temperature for 30-120 minutes to completely melt it to form a metallurgical grade silicon melt, and then using argon as the carrier gas for the nitriding agent Blown into metallurgical grade silicon melt for nitridation reaction.

Preferably, the specific steps of the third step are: spraying nitrogen gas on the outside of the silicon melt obtained in step 2 for forced cooling, then turning off the electromagnetic force to obtain the surrounding polysilicon rich in nitride particles, and then enriching the surrounding nitride-rich polysilicon The polycrystalline silicon of the particles is mechanically separated to obtain polycrystalline silicon rich in nitride particles and polycrystalline silicon after boron removal, respectively.

Preferably, the specific steps of the fourth step are: pulverizing the polycrystalline silicon rich in nitride particles obtained in the third step, adding ammonium chloride particles, and performing nitridation treatment in a fluid N ₂ atmosphere to obtain a silicon nitride product .

Preferably, the electromagnetic parameters of the electromagnetic purification are: current intensity 10-50A, voltage: 200-550V, frequency: 50-100kHz, power: 4-25kW, electromagnetic purification time: 10-180s.

Preferably, the nitriding agent is N ₂ and/or NH ₃ , the nitrogen concentration of the nitriding agent ranges from 0.1 to 10%, and the nitriding time is 5 to 180 s.

Preferably, in the fourth step, the interface between the polysilicon of the nitride-rich particles and the polysilicon with low boron impurities in the center is mechanically separated from the surface of the polysilicon obtained in the third step to 5-15 mm inside.

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 thereof is 1-30 μm.

Preferably, the polycrystalline silicon rich in silicon nitride particles is pulverized to a particle size range of 10-50 μm, the amount of ammonium chloride added is 20 to 100% of the mass of the polycrystalline silicon rich in silicon nitride particles, and the ammonium chloride particles are The diameter ranges from 10 to 50 μm.

Preferably, the temperature range of the nitriding treatment is 600-1200° C., the flow rate of fluid N ₂ is 100-500 mL/min, and the nitriding time is 20-180 min.

3. Beneficial effects

Adopting the technical scheme provided by the present invention, compared with the existing known technology, has the following remarkable effects:

(1) A method for nitriding-purifying removal of boron impurities in metallurgical silicon of the present invention, adding a nitriding agent to metallurgical grade silicon melt, and the addition of the nitriding agent can convert boron impurities in the silicon melt into nitrogen Then, electromagnetic force is applied to the nitrided silicon melt to gather the nitride particles around the silicon melt, and then the silicon melt and impurities are forcibly cooled and separated, and the silicon material from which the nitride particles are separated is used. to produce silicon nitride; due to the obvious difference in conductivity between the nitride particles and the silicon melt, under the action of electromagnetic force, the nitride particles will be enriched around the melt, thereby realizing boron impurities and silicon melt. effective separation;

(2) A method for nitriding-purifying removal of boron impurities in metallurgical silicon of the present invention, pulverizing polysilicon rich in silicon nitride particles, adding ammonium chloride particles in addition _; nitriding treatment in a fluid N atmosphere The silicon nitride product is obtained; the polysilicon rich in nitride particles is rationally utilized and subjected to nitridation treatment, which can realize the efficient utilization of resources and improve the technical economy;

(3) In a method for nitriding-purifying and removing boron impurities in metallurgical silicon of the present invention, an electromagnetic force is applied to the nitrided melt, and the nitrides are enriched around the nitrided melt under the action of the electromagnetic force, thereby realizing the nitrided melt. Separation from silicon melt; electromagnetic purification only relies on the action of electromagnetic external field to separate nitride particles from melt. It is a non-contact and clean refining technology, which will not introduce new media into silicon melt. In addition, the electromagnetic purification process only needs to adjust parameters such as current intensity for efficient separation of nitride particles and silicon melt, with simple operation, low cost and high boron removal efficiency.

Description of drawings

FIG. 1 is a schematic diagram of a method for nitriding-purifying removal of impurities in metallurgical silicon according to the present invention.

Detailed ways

The following detailed description and example embodiments of the invention can be better understood in conjunction with the accompanying drawings, wherein elements and features of the invention are identified by reference numerals.

Example 1

With reference to FIG. 1 , a method for nitriding-purifying removal of boron impurities in metallurgical silicon in this embodiment includes the following steps: adding a nitriding agent to metallurgical grade silicon melt, and then nitriding the silicon melt after nitriding. Electromagnetic force is applied to aggregate the nitride particles around the silicon melt, and the silicon melt and the nitride particles are forcedly cooled and separated, and the separated, nitride-rich silicon material is used to produce silicon nitride. The specific steps are:

Step 1: Nitriding blowing

First, the metallurgical grade silicon is heated to above the melting point of silicon and kept for 30-120 minutes to make it melt completely to form a metallurgical grade silicon melt. In this embodiment, the metallurgical grade silicon is heated to 1650°C, and the holding time is 120 minutes. The selected metallurgical grade silicon is pure is 95%, and the boron impurity content is 500ppm; then the nitriding agent is blown into the metallurgical grade silicon melt with argon as the carrier gas to carry out the nitriding reaction, wherein the nitriding agent is N ₂ and/or NH ₃ , and the nitriding agent is The nitrogen concentration range of the agent is 0.1-10%, and the nitriding time is 5-180s. The nitriding agent used in this example is N ₂ , the N concentration is 1%, and the nitriding time is 180s;

It should be noted that adding a nitriding agent to metallurgical grade silicon can make impurities boron nitrided into BN, and BN exists in the form of solid particles in the silicon melt, which is insoluble in the silicon melt and can be removed from the silicon melt. In addition, since Si is the matrix, the probability of its reaction with the nitriding agent is much greater than the probability of the reaction between B and N, so the number of Si ₃ N ₄ particles generated by the reaction of Si and N in the silicon melt is more than the number of BN particles. The Si ₃ N ₄ particles will further adsorb the unreacted boron impurities in the silicon melt, nitriding to form Si ₃ N ₄ -BN composite particles, and the boron in the melt is mainly adsorbed by Si ₃ N ₄ and nitrided to remove boron Impurities predominate.

It should be further explained that the nitriding agent used in this embodiment is N ₂ , which can not only be used to generate BN particles and Si ₃ N ₄ -BN composite particles, but also exist in the form of bubbles in the silicon melt with the carrier gas Ar, The bubbles dispersed in the silicon melt are beneficial to adsorb BN particles, Si ₃ N ₄ particles and Si ₃ N ₄ -BN composite particles, and promote the removal of B impurities from the silicon melt;

Step 2: Electromagnetic Purification

Applying electromagnetic force to the nitrided melt obtained after the nitridation reaction in step 1, to gather impurities around the silicon melt; wherein, the electromagnetic parameters of the electromagnetic force are: current intensity 10-50A, voltage: 200-550V, frequency: 50 ～100kHz, power: 4～25kW, electromagnetic purification time: 10～180s; specific to this embodiment, the current intensity is 50A, the voltage: 200V, the frequency: 50kHz, the power: 10kW, the purification time: 180s;

It is worth noting that due to the conversion of impurities in silicon into BN particles, Si ₃ N ₄ particles and Si ₃ N ₄ -BN composite particles, although these solid impurities can be gradually removed by floating up, their floating speed is slow and the efficiency is low. It cannot meet the production requirements, but there is a significant difference in conductivity between the solid phase particles and the silicon melt at high temperatures, and the solid phase particles that are non-conductive or poorly conductive under electromagnetic action are not affected by or are subject to very little electromagnetic force; Therefore, under the action of electromagnetic force, Si ₃ N ₄ particles, BN particles and Si ₃ N ₄ -BN composite particles generated in the nitriding blowing stage will be enriched to the outside, bottom and top of the melt;

The third step: cooling separation

The silicon melt obtained in step 2 is sprayed with nitrogen agent for forced cooling, and then the electromagnetic force is turned off to obtain surrounding polysilicon rich in nitride particles. In order to separate and remove the nitride particles, the above-mentioned surrounding polysilicon rich in nitride particles is mechanically separated. The purpose of turning off the electromagnetic force after forced cooling is to ensure that the outer or bottom and top of the silicon melt are solidified first, which ensures that the nitride particles are rich in the electromagnetic action. Collected in these first solidified parts;

Step 4: Silicon Nitride Preparation

The polysilicon rich in nitride particles obtained in the third step is pulverized to a particle size of 10-50 μm, and in this embodiment, the particle size is pulverized to 10 μm; in addition, ammonium chloride particles are added, and the amount added is the mass of the polycrystalline silicon rich in impurities 20-100% of the ammonium chloride particle size range is 10-50 μm; the silicon nitride product is obtained by nitriding in a fluid N ₂ atmosphere, wherein the temperature range of the nitriding treatment is 600-1200 ℃, and the fluidity The flow rate of N ₂ is 100-500 mL/min, and the nitriding time is 20-180 min. Specifically, in this embodiment, the nitriding temperature is 600°C, the flow rate of fluid N ₂ is 100 mL/min, and the nitriding time is 180 min;

It is worth noting that, in order to reasonably utilize the polysilicon rich in nitride particles, nitriding it can realize the efficient utilization of resources and improve the technical economy.

In this example, the content of polysilicon and boron impurities finally obtained is 20 ppm, and the purity of the silicon nitride product reaches 99%.

Example 2

This embodiment is basically the same as Embodiment 1, the difference is that in this embodiment, metallurgical grade silicon is heated to 1600° C. for 60 minutes, the metallurgical grade silicon has a purity of 99%, and the boron impurity content is 100 ppm. The nitriding agent used was NH ₃ , the N concentration was 5%, and the nitriding time was 120 s. In the second step, the current intensity is 40A, the voltage: 500V, the frequency: 80kHz, the power: 20kW, and the purification time: 120s. In the fourth step of this example, the polysilicon rich in nitride particles is pulverized to 30 μm, the mass of ammonium chloride particles is 50% of the mass of polysilicon rich in nitride particles, nitriding temperature: 800 ° C, fluidity N ₂ The flow rate was 200 mL/min, and the nitridation time was 90 min.

In this example, the content of polysilicon and boron impurities finally obtained is 5 ppm, and the purity of the silicon nitride product reaches 99.6%.

It is worth noting that the nitriding agent used in this embodiment is NH ₃ , which is different from N ₂ as the nitriding agent in that NH ₃ can generate N ₃ H ₆ B in addition to the reaction of impurity boron in silicon to generate BN _3. The substance exists in the form of gas phase in the silicon melt, which is not only easy to remove, but also can adsorb Si ₃ N ₄ particles, BN particles, and Si ₃ N ₄ -BN composite particles to float and remove together.

Example 3

This embodiment is basically the same as Embodiment 1, except that: this embodiment heats metallurgical grade silicon to 1500° C. for 40 minutes, the metallurgical grade silicon has a purity of 99.5%, and the boron impurity content is 50 ppm. The nitriding agents used were N ₂ and NH ₃ , the N concentration was 8%, and the nitriding time was 100s. In the second step, the current intensity is 35A, the voltage: 300V, the frequency: 70kHz, the power: 10.5kW, and the purification time: 60s. In the fourth step of this embodiment, the polysilicon rich in nitride particles is pulverized to 15 μm, the mass of ammonium chloride particles is 100% of that of the polysilicon rich in nitride particles, the nitridation temperature is 900°C, and the fluidity is N ₂ The flow rate was 300mL/min, and the nitridation time was 60min.

In this example, the content of polysilicon and boron impurities finally obtained is 3 ppm, and the purity of the silicon nitride product reaches 99.9%.

The present invention has been described in detail above with reference to specific exemplary embodiments. However, it should be understood that various modifications and variations can be made without departing from the scope of the present invention as defined by the appended claims. The detailed description and drawings are to be regarded in an illustrative rather than a restrictive sense, and if any such modifications and variations exist, they will fall within the scope of the invention described herein. In addition, the background art is intended to illustrate the research and development status and significance of the present technology, and is not intended to limit the present invention or the application and application fields of the present 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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