Method for preparing high-purity silicon tetrafluoride by dissociating fluosilicate through low-temperature plasma

Abstract

The invention relates to a method for preparing high-purity silicon tetrafluoride by dissociating fluosilicate through low-temperature plasma. The method comprises the following steps: crushing fluosilicate in a crusher, and heating and dewatering in a vibrated fluidized bed; the treated fluosilicate powder is conveyed to a plasma reactor through carrier gas to be dissociated to generate silicon tetrafluoride; and finally, silicon tetrafluoride generated by reaction enters a first-stage condenser to separate solid metal fluoride, then enters a cold hydrazine to be cooled for first-stage impurity removal, and then enters an adsorption tower for second-stage impurity removal, so that high-purity silicon tetrafluoride is obtained. The fluosilicate is dissociated by adopting a low-temperature plasma technology, so that high-purity silicon tetrafluoride is efficiently prepared under a low-temperature condition; meanwhile, the one-step method is short in conversion process, fluorine-containing waste is not generated, a simple purification step is combined, the production cost and the environment-friendly burden are reduced, the raw material adaptability is high, and operation is easy.

Description

A method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates Technical Field

[0001] This application belongs to the field of fluoride preparation technology, specifically relating to a method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates. Background Technology

[0002] Silicon tetrafluoride is mainly used in the electronics and semiconductor industries as a silicon nitride etchant, a P-type dopant, a silicon source for ion implantation processes, epitaxial deposition and diffusion, and a raw material for high-purity quartz glass for optical fibers. It is also an important raw material for the production of polycrystalline silicon and its derivatives, and can be used to prepare electronic-grade silanes or silicon.

[0003] Currently, the main methods for preparing silicon tetrafluoride are: (1) Direct synthesis of elemental silicon and fluorine: High-purity elemental silicon reacts directly with fluorine to generate silicon tetrafluoride gas. This method requires high purity of fluorine, and fluorine is chemically active and highly corrosive. It can react with most metals at room temperature, which requires high-quality equipment and high cost of producing fluorine. Therefore, it is not suitable for industrial production.

[0004] (2) Sulfuric acid method: HF is produced by reacting fluorite (CaF2) with sulfuric acid, and then synthesized with SiO2 to form silicon tetrafluoride. This process has a long production process, high energy consumption and generates a large amount of waste residue.

[0005] (3) Fluorosilicate pyrolysis: Under high temperature conditions, fluorosilicates are thermally decomposed to generate silicon tetrafluoride and fluoride salts, such as Na2SiF6→SiF4+2NaF. The reaction temperature needs to be >500℃, the reaction is incomplete, and the byproduct NaF encapsulates the raw materials, hindering mass transfer.

[0006] (4) Hydrofluoric acid method: Silicon powder and hydrogen fluoride gas react directly at high temperature. This method may be more direct and has the advantages of high conversion rate, low energy consumption and large output, but the reaction conditions may be more stringent, the cost of anhydrous HF and high-purity silicon powder is high, and the equipment is severely corroded, which limits its promotion and application.

[0007] In addition, there are some improved preparation methods in the existing technology. For example, application CN102390835A discloses a method for preparing silicon tetrafluoride from calcium fluorosilicate. This method uses hydrated calcium fluorosilicate as raw material, which is preheated and dehydrated, then pyrolyzed at 220-420℃, and then purified by sulfuric acid washing to obtain silicon tetrafluoride with a purity greater than 99%. Although this technical solution reduces the pyrolysis temperature and alleviates equipment corrosion, the pyrolysis process still requires a relatively high temperature, resulting in significant energy consumption. Furthermore, the use of sulfuric acid washing may introduce wastewater treatment problems, and the limited source of calcium fluorosilicate may affect the economics of industrial production.

[0008] Application CN110282630A discloses a method for producing silicon tetrafluoride from fluorosilicates. This method involves reacting fluorosilicates with a liquid containing hydrogen fluoride at low temperatures (-30~50℃) to generate silicon tetrafluoride and fluoride salts, followed by purification through gas separation and solid-liquid separation. While this technique achieves a low-temperature reaction and mild operating conditions, reducing byproducts, it requires high-purity hydrogen fluoride, resulting in higher raw material costs. The strong corrosiveness of hydrogen fluoride still places high demands on equipment materials, and improper moisture control during the reaction can easily lead to hydrolysis of silicon tetrafluoride, generating impurities and increasing the difficulty of purification.

[0009] Application CN110606490B discloses a method for synthesizing and purifying high-purity silicon tetrafluoride. This method prepares crude silicon tetrafluoride through a fluorosilicate pyrolysis reaction (300-500℃), then removes moisture and acidic gases using an adsorption stage, controls the polymerization of fluorosilicone ethers through adsorption, and finally separates the azeotropic substances through distillation and complex distillation to obtain a high-purity product. This technical solution improves conversion rate and purity, but the pyrolysis temperature remains high, resulting in high energy consumption. Furthermore, the purification process is complex, involving multiple adsorption and distillation steps, leading to high equipment investment and operating costs, and potential secondary pollution, making it unsuitable for large-scale, low-cost production. In summary, existing technologies suffer from high production costs, high-temperature energy consumption, equipment corrosion susceptibility, low conversion rates, and large amounts of waste residue and wastewater, resulting in high environmental governance costs. Therefore, there is an urgent need to propose a simple, fast, and low-energy-consumption method for preparing silicon tetrafluoride suitable for industrial production to address the problems existing in current technologies. Summary of the Invention

[0010] In view of the problems existing in the prior art, such as high production cost, high energy consumption at high temperature, easy corrosion of equipment, low conversion rate, large amount of waste residue and wastewater generated and high environmental protection treatment cost, this application proposes a method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates.

[0011] The technical solution of this application is as follows: A method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates, comprising the following steps: Step S1. Fluorosilicate crushing and dehydration: Fluorosilicates are added to a pulverizer for crushing, followed by dehydration; Step S2. Fluorosilicates dissociate in a plasma field to generate silicon tetrafluoride: The fluorosilicate powder processed in Step S1 is transported to a plasma reactor by a carrier gas for dissociation to generate silicon tetrafluoride; Step S3. Gas purification: The silicon tetrafluoride generated by the reaction enters a primary condenser to separate solid metal fluorides, then enters a cold hydrazine for cooling and primary impurity removal, and then enters an adsorption tower for secondary impurity removal to obtain high-purity silicon tetrafluoride.

[0012] Preferably, the particle size of the fluorosilicate after pulverization in step S1 is 100~300 mesh.

[0013] Preferably, the water content of the fluorosilicate powder after dehydration in step S1 is 20~50 ppm.

[0014] Preferably, the carrier gas in step S2 is an inert gas Ar or N2, with a purity ≥99.9%, a pressure of 0.1~0.5 MPa, and a flow rate of 20-30 L / min.

[0015] Preferably, in step S2, the plasma is a microwave or radio frequency source with a power density of 0.5~3 kW / cm³, a reaction temperature of 150~350℃, and a reaction pressure of 0.1~0.5 MPa.

[0016] Preferably, in step S3, the temperature of the primary condenser is -30 to -0°C, and the pressure is 0.1 to 0.5 MPa.

[0017] Preferably, in step S3, the temperature of the cold hydrazine is -150 to -100°C, and the pressure is 0.1 to 1.6 MPa.

[0018] Preferably, the adsorption tower in step S3 is a molecular sieve adsorption tower, which is filled with 5A molecular sieve, and the operating temperature is -50~0℃, and the pressure is 0.1~1.6 MPa.

[0019] Preferably, the plasma reactor is lined with a fluorine-resistant material.

[0020] Preferably, the fluorosilicate is sodium fluorosilicate or calcium fluorosilicate.

[0021] The beneficial effects of this application are as follows: (1) This application employs a non-equilibrium plasma field in which fluorosilicate raw materials are bombarded by high-energy electrons to selectively dissociate the molecular bonds of fluorosilicate, thus avoiding overall high-temperature pyrolysis. The plasma power density is controlled at 0.5~3 kW / cm³, ensuring efficient dissociation while maintaining a low-temperature environment, thus avoiding the stringent requirements on equipment imposed by traditional high-temperature pyrolysis. In addition, the reactor is lined with fluorine-resistant material, which further enhances the corrosion resistance and service life of the equipment.

[0022] (2) This application realizes a one-step direct conversion of fluorosilicates into silicon tetrafluoride gas and metal fluoride solids, eliminating intermediate steps and shortening the process flow. All F elements are converted into silicon tetrafluoride and fluoride salts, with a high conversion rate and no fluoride-containing wastewater or waste residue is generated, resulting in low environmental treatment costs. The use of a primary condenser, cold hydrazine, and molecular sieve adsorption tower ensures high product purity and reduces the burden of subsequent processing.

[0023] (3) The reaction temperature of this application is controlled at 150~350℃, which is lower than that of conventional fluorosilicate pyrolysis (usually requiring >500℃), resulting in lower energy consumption. At the same time, the reaction pressure is 0.1~0.5 MPa, which reduces the corrosiveness to equipment materials and further extends the equipment life. High-purity inert gas is used as the carrier gas, ensuring the stability and safety of the reaction.

[0024] (4) The raw materials used in this application are widely applicable and can process various fluorosilicates such as sodium fluorosilicate or calcium fluorosilicate. The reaction process is simple and does not require the participation of catalysts or other materials, thus reducing the possibility of impurities.

[0025] (5) This application has fewer steps and lower equipment requirements, such as mild reaction conditions, which greatly reduces production costs. No complex pretreatment or posttreatment is required, resulting in low costs and suitability for industrial production. Attached Figure Description

[0026] Figure 1 is a process flow diagram for preparing high-purity silicon tetrafluoride according to this application. Detailed Implementation

[0027] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0028] Example 1 This example provides a method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates. The process flow is shown in Figure 1, including the following steps: Step S1. Sodium fluorosilicate crushing and dehydration: Sodium fluorosilicate raw material is added to a pulverizer for crushing. After crushing, the particle size of sodium fluorosilicate is 100~150 mesh. Then it enters a vibrating fluidized bed for drying and heating to remove water to 20~30 ppm. After passing the pretreatment, it enters the silo. The silo is sealed (using nitrogen sealing) to prevent the raw material from reabsorbing moisture from the environment.

[0029] Step S2. Sodium fluorosilicate dissociates in a plasma field to generate silicon tetrafluoride.

[0030] To prevent the reactor from reacting with fluorine gas, the plasma reactor should be made of a material that can resist gas corrosion. In this embodiment, the reactor is made of a chromium-nickel-molybdenum alloy.

[0031] Turn on the microwave plasma reactor power supply, select a power density of 0.5 kW / cm³, and set the reaction temperature to 150~200℃.

[0032] Open the N2 carrier gas valve. The N2 purity is ≥99.99% (using purified N2 reduces the introduction of H2O, reduces the generation of HF, and reduces equipment corrosion). Select a carrier gas pressure of 0.1~0.2MPa and a flow rate of 20~30 L / min.

[0033] When the outlet valve of the silo is opened, sodium fluorosilicate powder is transported to the plasma reactor through the carrier gas N2. In the plasma field environment, sodium fluorosilicate dissociates, mainly producing silicon tetrafluoride and sodium fluoride, as well as a small amount of other metal fluorides and metal oxides.

[0034] The chemical reaction is: Na2SiF6 → SiF4 + 2NaF. Step S3. Gas purification: The reactants enter the primary condenser, which has a temperature of -30 to -25°C. Sodium fluoride and a small amount of metal fluorides and metal oxides are condensed into solids and deposited at the bottom of the condenser. Gaseous silicon tetrafluoride and a small amount of non-condensable gases enter the cold hydrazine from the top of the condenser for further cooling.

[0035] The cold hydrazine is cooled with liquid nitrogen, with an operating temperature of -150 to -120°C and a pressure of 0.1 to 1.2 MPa. Silicon tetrafluoride, with a melting point of -90.2°C, is deposited at the bottom of the cold hydrazine, while non-condensable gaseous impurities such as O2 and N2 are discharged from the top of the cold hydrazine.

[0036] After the cold hydrazine was collected, the cold hydrazine feed valve was closed. The cold hydrazine was then heated to -10 to 0°C. The gaseous crude silicon tetrafluoride gas was then introduced into a 5A molecular sieve adsorption tower to remove trace impurities such as HF, O2, and N2, yielding high-purity SiF4. The high-purity silicon tetrafluoride was then analyzed using a GC6600 gas chromatograph, and the results are shown in Table 1.

[0037] Example 2 This example provides a method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates. The process flow is shown in Figure 1, including the following steps: Step S1. Sodium fluorosilicate crushing and dehydration: Calcium fluorosilicate raw material is added to a pulverizer for crushing. After crushing, the particle size of calcium fluorosilicate is 150~200 mesh. Then it enters a vibrating fluidized bed for drying, and is heated to remove water to 30~40 ppm. After passing the pretreatment, it enters the silo, which is sealed (using nitrogen sealing) to prevent the raw material from reabsorbing moisture from the environment.

[0038] Step S2. Sodium fluorosilicate dissociates in a plasma field to generate silicon tetrafluoride.

[0039] To prevent the reactor from reacting with fluorine gas, the plasma reactor should be made of a material that can resist gas corrosion. In this embodiment, the reactor is made of a chromium-nickel-molybdenum alloy.

[0040] Turn on the microwave plasma reactor power supply, select a power density of 1 kW / cm³, and set the reaction temperature to 200~250℃.

[0041] Open the N2 carrier gas valve. The N2 purity should be ≥99.99% (using purified N2 reduces the introduction of H2O, decreases HF generation, and reduces equipment corrosion). Select a carrier gas pressure of 0.2~0.3MPa and a flow rate of 20~30 L / min.

[0042] When the outlet valve of the silo is opened, the calcium fluorosilicate powder is transported to the plasma reactor through the carrier gas N2. In the plasma field environment, the calcium fluorosilicate dissociates, mainly producing silicon tetrafluoride and calcium fluoride, as well as a small amount of other metal fluorides and metal oxides.

[0043] The chemical reaction is: CaSiF6 → SiF4 + CaF2. Step S3. Gas purification: The reactants enter the primary condenser, with a condenser temperature of -30 to -25℃. Calcium fluoride and small amounts of metal fluorides and metal oxides are condensed into solids and deposited at the bottom of the condenser. Gaseous silicon tetrafluoride and a small amount of non-condensable gases enter the cold hydrazine from the top of the condenser for further cooling. The cold hydrazine is cooled with liquid nitrogen, with an operating temperature of -150 to -120℃ and a pressure of 0.1 to 1.2 MPa. Silicon tetrafluoride has a melting point of -90.2℃ and deposits at the bottom of the cold hydrazine. Non-condensable gaseous impurities such as O2 and N2 are discharged from the top of the cold hydrazine.

[0044] After the cold hydrazine collection was completed, the cold hydrazine feed valve was closed. The cold hydrazine was then heated to -10 to 0°C. The gaseous crude silicon tetrafluoride gas was then introduced into a 5A molecular sieve adsorption tower to remove trace impurities such as HF, O2, and N2, yielding high-purity SiF4. The high-purity silicon tetrafluoride was then analyzed using a GC6600 gas chromatograph, and the results are shown in Table 1.

[0045] Example 3 This example provides a method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates. The process flow is shown in Figure 1, including the following steps: Step S1. Sodium fluorosilicate crushing and dehydration: Sodium fluorosilicate raw material is added to a pulverizer for crushing. After crushing, the particle size of sodium fluorosilicate is 200~250 mesh. Then it enters a vibrating fluidized bed for drying and heating to remove water to 40~50 ppm. After passing the pretreatment, it enters the silo. The silo is sealed (using nitrogen sealing) to prevent the raw material from reabsorbing moisture from the environment.

[0046] Step S2. Sodium fluorosilicate dissociates in a plasma field to generate silicon tetrafluoride.

[0047] To prevent the reactor from reacting with fluorine gas, the plasma reactor should be made of a material resistant to gas corrosion. In this embodiment, the reactor is made of a chromium-nickel-molybdenum alloy.

[0048] Turn on the microwave plasma reactor power supply, select a power density of 1.5 kW / cm³, and set the reaction temperature to 250~300℃.

[0049] Open the N2 carrier gas valve. The N2 purity should be ≥99.99% (using purified N2 reduces the introduction of H2O, decreases HF generation, and reduces equipment corrosion). Select a carrier gas pressure of 0.2~0.3MPa and a flow rate of 20~30 L / min.

[0050] When the outlet valve of the silo is opened, sodium fluorosilicate powder is transported to the plasma reactor through the carrier gas N2. In the plasma field environment, sodium fluorosilicate dissociates, mainly producing silicon tetrafluoride and sodium fluoride, as well as a small amount of other metal fluorides and metal oxides.

[0051] Step S3. Gas Purification: The reactants enter the primary condenser, with a condenser temperature of -20 to -10°C. Sodium fluoride and small amounts of metal fluorides and metal oxides are condensed into solids and deposited at the bottom of the condenser. Gaseous silicon tetrafluoride and a small amount of non-condensable gases enter the cold hydrazine from the top of the condenser for further cooling. The cold hydrazine is cooled with liquid nitrogen at an operating temperature of -120 to -100°C and a pressure of 0.1 to 1.2 MPa. Silicon tetrafluoride, with a melting point of -90.2°C, deposits at the bottom of the cold hydrazine, while non-condensable gaseous impurities such as O2 and N2 are discharged from the top of the cold hydrazine.

[0052] After the cold hydrazine collection was completed, the cold hydrazine feed valve was closed. The cold hydrazine was then heated to -20 to -10°C. The gaseous crude silicon tetrafluoride gas was then introduced into a 5A molecular sieve adsorption tower to remove trace impurities such as HF, O2, and N2, yielding high-purity silicon tetrafluoride. The high-purity silicon tetrafluoride was then analyzed using a GC6600 gas chromatograph, and the results are shown in Table 1.

[0053] Example 4 This example provides a method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates. The process flow is shown in Figure 1, including the following steps: Step S1. Crushing and dehydrating calcium fluorosilicate: The calcium fluorosilicate raw material is added to a pulverizer for crushing. After crushing, the particle size of the calcium fluorosilicate is 250~300 mesh. Then it enters a vibrating fluidized bed for drying and heating to remove water to 20~30 ppm. After passing the pretreatment, it enters the silo. The silo is sealed (using nitrogen sealing) to prevent the raw material from reabsorbing moisture from the environment.

[0054] Step S2. Calcium fluorosilicate dissociates in a plasma field to form silicon tetrafluoride.

[0055] To prevent the reactor from reacting with fluorine gas, the plasma reactor should be made of a material resistant to gas corrosion. In this embodiment, the reactor is made of a chromium-nickel-molybdenum alloy.

[0056] Turn on the microwave plasma reactor power supply, and select a power density of 3 kW / cm². 3 The reaction temperature is set to 300~350℃.

[0057] Open the N2 carrier gas valve. The N2 purity should be ≥99.99% (using purified N2 reduces the introduction of H2O, decreases HF generation, and reduces equipment corrosion). Select a carrier gas pressure of 0.2~0.3MPa and a flow rate of 20~30 L / min.

[0058] When the outlet valve of the silo is opened, the calcium fluorosilicate powder is transported to the plasma reactor through the carrier gas N2. In the plasma field environment, the calcium fluorosilicate dissociates, mainly producing silicon tetrafluoride and calcium fluoride, as well as a small amount of other metal fluorides and metal oxides.

[0059] Step S3. Gas Purification: The reactants enter the primary condenser, with a condenser temperature of -20 to -10°C. Calcium fluoride and small amounts of metal fluorides and metal oxides are condensed into solids and deposited at the bottom of the condenser. Gaseous silicon tetrafluoride and a small amount of non-condensable gases enter the cold hydrazine from the top of the condenser for further cooling. The cold hydrazine is cooled with liquid nitrogen at an operating temperature of -120 to -100°C and a pressure of 0.1 to 1.2 MPa. Silicon tetrafluoride, with a melting point of -90.2°C, deposits at the bottom of the cold hydrazine, while non-condensable gaseous impurities such as O2 and N2 are discharged from the top of the cold hydrazine.

[0060] After collecting a certain amount of cold hydrazine (calculated by weight or feed flow rate), the cold hydrazine feed valve is closed. The cold hydrazine is then heated to -20 to -10°C, and the gaseous crude silicon tetrafluoride gas enters a 5A molecular sieve adsorption tower to remove trace impurities such as HF, O2, and N2, yielding high-purity silicon tetrafluoride. The high-purity silicon tetrafluoride was then analyzed using a GC6600 gas chromatograph, and the results are shown in Table 1.

[0061] The difference between Comparative Example 1 and Example 1 is that the reaction temperature of Comparative Example 1 is 500°C.

[0062] The difference between Comparative Example 2 and Example 1 is that the reaction pressure in Comparative Example 2 is 1.5 MPa.

[0063] Table 1. Sample HF content (ppmV) N2+O2 content (ppmV) H2 content (ppmV) CO content (ppmV) CO2 content (ppmV) CH4 content (ppmV) Example 1 1.24 1.02 1.20 0.08 1.30 1.55 Example 2 1.55 1.65 1.65 0.1 1.15 1.22 Example 3 1.82 1.28 1.02 0.05 1.05 1.35 Example 4 1.32 0.80 1.10 0.06 1.45 1.25 Comparative Example 1 2.56 3.17 2.75 0.26 2.43 2.89 Comparative Example 2 3.14 2.99 2.84 0.35 2.51 3.07 Table Notes: 1. Data sourced from GC6600 gas chromatograph and infrared ion chromatograph.

[0064] As can be seen from Examples 1-4, Comparative Examples 1-2, and Table 1, the preparation method of this application achieves a high yield of silicon tetrafluoride. All the reaction products of the above examples exhibit high selectivity and low amounts of byproducts. Examples 1-4 show that the moisture content of the raw materials has a certain influence on the HF content; higher moisture content results in a higher HF content in the product. Reaction temperature, pressure, and raw material particle size have relatively low effects on the product.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates, characterized in that, The process includes the following steps: Step S1. Fluorosilicon crushing and dehydration: Fluorosilicon is crushed in a pulverizer and then dehydrated; Step S2. Fluorosilicon dissociation in a plasma field to generate silicon tetrafluoride: The fluorosilicate powder processed in Step S1 is transported to a plasma reactor by a carrier gas to dissociate and generate silicon tetrafluoride; Step S3. Gas purification: The silicon tetrafluoride generated by the reaction enters a primary condenser to separate solid metal fluorides, then enters a cold hydrazine for cooling and primary impurity removal, and then enters an adsorption tower for secondary impurity removal to obtain high-purity silicon tetrafluoride.

2. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, In step S1, the particle size of the fluorosilicate after pulverization is 100~300 mesh.

3. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, In step S1, the water content of the fluorosilicate powder after dehydration is 20~50 ppm.

4. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, In step S2, the carrier gas is an inert gas, either Ar or N2, with a purity ≥99.9%, a pressure of 0.1~0.5MPa, and a flow rate of 20-30 L / min.

5. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, In step S2, the plasma is a microwave or radio frequency source with a power density of 0.5~3 kW / cm³, a reaction temperature of 150~350℃, and a reaction pressure of 0.1~0.5 MPa.

6. The method according to claim 1, characterized in that, In step S3, the temperature of the primary condenser is -30 to -0℃, and the pressure is 0.1 to 0.5 MPa.

7. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, In step S3, the temperature of the cold hydrazine is -150 to -100°C, and the pressure is 0.1 to 1.6 MPa.

8. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, In step S3, the adsorption tower is a molecular sieve adsorption tower, which is filled with 5A molecular sieve, and the operating temperature is -50~0℃, and the pressure is 0.1~1.6 MPa.

9. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, The plasma reactor is lined with a fluorine-resistant material.

10. The method for preparing high-purity silicon tetrafluoride by low-temperature plasma dissociation of fluorosilicates according to claim 1, characterized in that, The fluorosilicate is sodium fluorosilicate or calcium fluorosilicate.

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