Method for preparing low-dielectric fluorine-doped silicon dioxide aerogel from fluorine-containing silicon slag

Abstract

The invention discloses a method for preparing low-dielectric fluorine-doped silicon dioxide aerogel from fluorine-containing silicon slag, and belongs to an aerogel preparation method in the field of communication materials.According to the technical scheme, the fluorine-containing silicon slag is dried, ground into fine powder and sieved, and reacts with sodium hydroxide to prepare a sodium fluosilicate solution; the preparation method comprises the following steps: preparing wet gel by adopting a gel-sol method or a template method, and then aging and drying to obtain F-doped SiO2 aerogel; in the aging step, wet gel is placed in an aging agent solution to be soaked for 5-10 days at the temperature of 5-30 DEG C, then the wet gel is soaked and washed in deionized water for multiple times to clean impurity ions in the wet gel, and finally the wet gel is soaked and washed in a replacement solvent for multiple times to replace water in the wet gel. According to the preparation method, industrial solid waste-fluorine-containing silicon slag is taken as a raw material, the production cost is low, the process difficulty is low, and the prepared F-doped SiO2 aerogel is few in residual impurities, excellent in pore structure and low in dielectric constant.

Description

TECHNICAL FIELD

[0001] The application relates to the preparation of aerogels of communication materials, in particular to a preparation method of fluorine-doped silicon dioxide aerogels. BACKGROUND

[0002] Compared with 4G communication, 5G communication uses electromagnetic waves with a relatively higher frequency, and the higher the frequency of electromagnetic waves, the shorter the wavelength, the poorer the diffraction ability, and the greater the attenuation of electromagnetic waves in the propagation process. Therefore, the transmission ability of 5G communication electromagnetic waves is lower than that of 4G communication. According to Maxwell's equations, the transmission speed and transmission loss rate of electromagnetic signals are closely related to the dielectric constant of the transmission medium material. Low dielectric constant materials are helpful to the transmission of electromagnetic signals. In recent years, in order to meet the needs of 5G high-frequency communication, the design and development of low dielectric constant materials have become a research hotspot.

[0003] The structure of Si-O tetrahedron of silicon dioxide gives it a low dielectric constant, and studies have shown that the introduction of nanopores into SiO2 to make aerogels can further reduce its dielectric constant to about 1.0. The low dielectric constant makes SiO2 aerogels play an important role in the electronic industry and are widely used in communication antennas, radar protective covers, load protection of various aerospace, and many other fields.

[0004] Fluorine-containing silicon slag is a high-silicon solid waste containing fluorine produced in the production of anhydrous hydrogen fluoride from fluorosilicic acid byproduct in phosphorus chemical industry, and the main component is silicon dioxide (about 80%, in addition to fluorine about 20%). At present, the treatment of fluorine-containing silicon slag is mainly stacking. Due to the strong corrosion and toxicity of fluorine, long-term stacking poses a threat to the safety of groundwater and soil. The current public use of fluorine-containing silicon slag is to separate fluorine from silicon slag through processes such as water washing, filtration and drying, and then further process into downstream products such as white carbon black, water glass and ammonium bifluoride. However, the fluorine removal is difficult and the defluorination process such as water washing is complex, making the economy poor. If the fluorine-containing silicon slag does not need to be defluorinated, it can be prepared into products with high added value, and the fluorine therein does not affect or even improves some key properties of the products, which has social and economic double benefits.

[0005] Studies have shown that the introduction of low-polarity groups or atoms into materials can reduce the dielectric constant of the system. The electronegativity of fluorine atom is 3.98, and the electronegativity of oxygen atom is 3.44, that is, the electron-withdrawing ability of fluorine atom is stronger than that of oxygen atom, and the bond formation ability of Si-F bond is stronger than that of Si-O bond. In view of this, F atoms have the ability to replace oxygen atoms into SiO2 lattice, and doping F atoms in SiO2 lattice can inhibit the orientation polarization of SiO2 internal dipole, thereby further reducing its dielectric constant.

[0006] SiO2 aerogel is usually prepared by sol-gel method, and the precursor silicon source includes two categories of organic silicon source and inorganic silicon source, wherein the organic silicon source is represented by methyl orthosilicate and ethyl orthosilicate, and the inorganic silicon source is represented by water glass. Compared with the organic silicon source, the inorganic silicon source is low in price and safe and non-toxic, and has an advantage in large-scale production and commercial use of SiO2 aerogel. For example, patent No. 202211278180.0 discloses a method for preparing SiO2 aerogel based on alkaline environment, which comprises the following steps: a. taking deionized water as a solvent, diluting water glass, mixing uniformly under ice bath condition, then slowly adding an acid catalyst treated by ice bath, stirring uniformly to obtain a low-temperature aerogel precursor, and the pH value of the aerogel precursor is 9-10; b. placing the aerogel precursor in a room temperature environment, and waiting for the aerogel precursor to form a wet gel; c. placing the wet gel in a constant temperature oven, and using a trimethylchlorosilane ethanol solution for multiple solvent replacement; d. placing the wet gel in a carbon dioxide supercritical drying kettle for supercritical drying to obtain SiO2 aerogel. The use of alkaline conditions reduces the corrosion of the supercritical drying equipment during the subsequent drying treatment of the wet gel, and improves the feasibility of industrial production.

[0007] Researchers hope to use fluorine-containing silicon slag as raw material to prepare low dielectric constant SiO2 aerogel for communication field, but the existing SiO2 aerogel preparation method has problems such as easy collapse of aerogel, poor pore structure and serious influence of residual conductive impurities on dielectric constant, so it is difficult to obtain the desired material. SUMMARY

[0008] The purpose of the present application is to solve the above technical problems, and provide a method for preparing low dielectric fluorine-doped SiO2 aerogel using industrial solid waste-fluorine-containing silicon slag as raw material. The method has low production cost and low process difficulty, and the prepared F-doped SiO2 aerogel has less residual impurities and excellent pore structure.

[0009] The technical scheme comprises the following steps: grinding the fluorine-containing silicon slag after drying to fine powder, sieving, reacting with sodium hydroxide aqueous solution to prepare fluorine-containing sodium silicate solution, preparing wet gel by sol-gel method or template method, then aging, drying to obtain F-doped SiO2 aerogel; In the aging step, the wet gel is soaked in the aging agent solution at 5-30℃ for 5-10d, then washed in deionized water for multiple times to remove impurity ions in the wet gel, and finally soaked in the displacement solvent to displace water in the wet gel.

[0010] The water content in the fluorine-containing silicon slag after drying control is less than 2wt%.

[0011] The preparation method of the sodium fluorosilicate solution is: stirring and dissolving the sieved fluorine-containing silicon residue in a 1-3 mol / L sodium hydroxide aqueous solution, and then filtering the undissolved residue to obtain a sodium fluorosilicate aqueous solution, and the concentration of the sodium fluorosilicate aqueous solution is 15-25 wt%.

[0012] The sol-gel method is: the sodium fluorosilicate solution is subjected to sodium removal treatment by a cation exchange resin to obtain a fluorosilicic acid aqueous solution, an alkaline catalyst is added to adjust the pH value to 4-8, and a wet gel is obtained by standing and reacting.

[0013] The template method is: the sodium fluorosilicate solution is subjected to sodium removal treatment by a cation exchange resin to obtain a fluorosilicic acid aqueous solution; the template solution is uniformly mixed with the fluorosilicic acid aqueous solution, an alkaline catalyst is added to the mixed solution to adjust the pH value to 4-8, and a wet gel is obtained by standing and reacting.

[0014] In the sol-gel method or the template method: after the alkaline catalyst is added to adjust the pH value, the wet gel is obtained by standing and reacting at 5-30℃ for 200-1000 min.

[0015] The alkaline catalyst is one of ammonia, NaOH, monoethanolamine, diethanolamine, and triethanolamine, and preferably the concentration of the aqueous solution thereof is 0.5-1.5 mol / L.

[0016] The template agent is one of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), polyacrylamide (PAM), carboxymethyl cellulose, polyethylene glycol (PEG), chitosan, collagen, and starch, the molecular weight thereof varies in the range of 5000-20000, the concentration of the aqueous solution thereof is 0.02-2 wt%, and the mass ratio of the template agent to the sodium fluorosilicate is (0.1-1):1.

[0017] In the aging step, each time the wet gel is soaked in deionized water for 1-2 d, and the soaking temperature in the displacement solvent is 5-30℃, and the soaking time is 3-5 d.

[0018] The aging agent solution is ethanol, or a mixed solution of ethanol and tetraethyl orthosilicate (TEOS) and / or water, and preferably the volume ratio of TEOS / ethanol is 1:3, or the volume ratio of TEOS / water / ethanol is 1:1:3.

[0019] The displacement solvent is one of methanol, acetone, ethanol, toluene, isopropanol, n-hexane, or n-heptane.

[0020] The drying method is freeze-drying or CO2 supercritical drying.

[0021] If the template method is used to prepare the wet gel, a template removal step is added after drying: the SiO2 aerogel obtained after drying is placed in a muffle furnace and calcined at high temperature in an air atmosphere to remove the polymer template, and then naturally cooled to obtain the F-doped SiO2 aerogel.

[0022] The calcination temperature is 500-1000° C., and the calcination time is 2-10 hours.

[0023] In response to the problems existing in the background technology, the present invention makes full use of the fluorine "impurities" in fluorine-containing silicon slag and introduces it into the SiO2 aerogel lattice as a modifier. By utilizing its intrinsic property that its electronegativity is stronger than that of oxygen, fluorine atoms replace oxygen vacancies and enter the silica lattice to further reduce the dielectric constant of the silica aerogel, thereby further reducing the dielectric constant of the SiO2 aerogel, in order to construct a low dielectric constant material that can be used in the field of 5G communications.

[0024] Furthermore, the inventors discovered that when using fluorine-containing silicon slag to prepare aerogels using conventional sol-gel or template methods, aerogel collapse is a common problem. In-depth analysis revealed that because the fluorine element in the fluorine-containing silicon slag has a stronger electronegativity than oxygen, the aerogel's three-dimensional network structure forms too quickly during preparation, easily leading to pore occlusion and ultimately collapse. Therefore, the present invention requires strict control of the gelation rate. Specifically, the wet gel is carefully immersed at low temperatures and for long periods during the sol-gel and aging steps to slow the formation of the aerogel's three-dimensional network structure, ensure sufficient pore formation, and avoid pore occlusion and ultimate collapse. During the sol-gel preparation stage, after adding an alkaline catalyst to adjust the pH, the reaction is allowed to stand at 5-30°C for 200-1000 minutes. During the aging stage, the immersion temperature in the aging agent is kept between 5-30°C, preferably between 10-15°C. Excessively high temperatures can cause aerogel collapse, while too low temperatures hinder gelation. Furthermore, if the low-temperature immersion time is too short, gelation is incomplete, while too long can cause pore collapse during drying.

[0025] Furthermore, the inventors also found that the addition of additives such as alkaline catalysts and aging agents during the preparation process would introduce impurity ions. These impurity ions act as carriers and seriously affect the dielectric constant. Therefore, after soaking in the aging agent in the aging step, the wet gel is soaked and washed multiple times in deionized water to clean out the impurity ions in the wet gel. Finally, the wet gel is soaked and washed in a displacement solvent to displace the water in the wet gel and remove the impurity ions.

[0026] Further analysis, because the pore structure of aerogel also seriously affect its dielectric constant, therefore preferably the introduction of molecular weight range in 5000-20000 template, this molecular weight conditions can better guide the formation of pores, too high molecular weight leads to small pores, but the molecular weight is too low will lead to unstable pore structure, and even lead to collapse; In drying, but also to use normal pressure drying, but using freeze drying or CO2 supercritical drying, using this drying method can avoid the capillary pressure generated by the volatilization of liquid inside the wet gel, so as to further optimize the pore structure and as far as possible to avoid the collapse of aerogel.

[0027] In summary, the present application uses industrial solid waste-fluorine-containing silicon slag as raw material, turning waste into treasure, and ingeniously introducing fluorine element into the three-dimensional network structure of silica aerogel. The dielectric constant is reduced by using the characteristic that the electronegativity of fluorine is higher than that of oxygen. At the same time, the problem of aerogel collapse caused by pore occlusion when fluorine is introduced is solved. The F-doped SiO2 aerogel prepared by the present application has the characteristics of low production cost, low process difficulty, less residual impurities, excellent pore structure, high specific surface area, high porosity and low dielectric constant.

[0028] Drawings Figure 1 The appearance of the F-doped SiO2 aerogel prepared in Example 5 is shown in the figure.

[0029] Figure 2 The SEM image of the F-doped SiO2 aerogel prepared in Example 5 is shown in the figure. DETAILED DESCRIPTION

[0030] The following examples further illustrate the technical solutions of the present application, but do not limit the scope of protection of the present application.

[0031] The specific surface area and porosity of the fluorine-containing silica aerogel in the present application are obtained by BET test, and nitrogen is used as the adsorbing gas.

[0032] The dielectric constant of the fluorine-containing silica aerogel in the present application is obtained by calculating the loss value and capacitance value of the sample tested by LCR impedance analyzer.

[0033] The percentage content involved in the following examples is mass percentage.

[0034] Example 1: The fluorine-containing silicon slag was dried in a vacuum oven at 110°C for 60 minutes, ground into fine powder and sieved, and the moisture content of the fluorine-containing silicon slag was controlled to be less than or equal to 2 wt% after drying. The fluorine content of the fluorine-containing silicon slag was determined to be 19.86 wt%. The pretreated fluorine-containing silicon slag was stirred and dissolved in a 1 mol / L sodium hydroxide aqueous solution, and then the undissolved residue was filtered to obtain a fluorine-containing sodium silicate aqueous solution with a concentration of 20 wt%. The fluorine-containing sodium silicate solution was subjected to sodium removal treatment by a styrene cation exchange resin to obtain a fluorine-containing silicic acid aqueous solution. 1 mol / L ammonia water was added to the solution to adjust the pH value to 5.8, and the solution was left to stand at 12°C for 400 minutes to obtain a wet gel.

[0035] The wet gel was soaked in anhydrous ethanol solution at 30°C for 5 days, and then impurity ions in the gel were washed out by soaking and washing in deionized water for 3 times, each time for 1 day. Finally, water in the wet gel was replaced by soaking in n-hexane at 30°C for 3 days to obtain a SiO2 wet gel.

[0036] The F-doped SiO2 aerogel was obtained by freeze-drying the SiO2 wet gel.

[0037] The specific surface area and porosity of the fluorine-containing silica aerogel prepared in this example were 436 m 2 / g and 93.6%, respectively, and the dielectric constant at 1000 Hz was 1.78.

[0038] Example 2: The fluorine-containing silicon slag was dried in a vacuum oven at 110°C for 60 minutes, ground into fine powder and sieved, and the moisture content of the fluorine-containing silicon slag was controlled to be less than or equal to 2 wt% after drying. The fluorine content of the fluorine-containing silicon slag was determined to be 19.86 wt%. The pretreated fluorine-containing silicon slag was stirred and dissolved in a 1 mol / L sodium hydroxide aqueous solution, and then the undissolved residue was filtered to obtain a fluorine-containing sodium silicate aqueous solution with a concentration of 20 wt%. The fluorine-containing sodium silicate solution was subjected to sodium removal treatment by a styrene cation exchange resin to obtain a fluorine-containing silicic acid aqueous solution. 1 mol / L ammonia water was added to the solution to adjust the pH value to 5.8, and the solution was left to stand at 12°C for 400 minutes to obtain a wet gel.

[0039] The wet gel was soaked in anhydrous ethanol solution at 30°C for 5 days, and then impurity ions in the gel were washed out by soaking and washing in deionized water for 3 times, each time for 1 day. Finally, water in the wet gel was replaced by soaking in n-hexane at 30°C for 3 days to obtain a SiO2 wet gel.

[0040] The F-doped SiO2 aerogel was obtained by freeze-drying the SiO2 wet gel.

[0041] The specific surface area and porosity of the fluorine-containing silica aerogel prepared in this example were 520 m2 / g and 94.2%, respectively, and the dielectric constant at 1000 Hz was 1.58.

[0042] Example 3 The fluorine-containing silicon slag was dried in a vacuum oven at 110°C for 60 min, ground into fine powder, and sieved. The fluorine content in the fluorine-containing silicon slag was determined to be 19.86 wt%. The pretreated fluorine-containing silicon slag was stirred and dissolved in 1 mol / L sodium hydroxide aqueous solution, and then the undissolved residue was filtered to obtain a fluorine-containing sodium silicate aqueous solution with a concentration of 15 wt%. The fluorine-containing sodium silicate solution was subjected to sodium removal treatment by using a styrene cation exchange resin to obtain a fluorine-containing silicic acid aqueous solution. 1 mol / L ammonia water was added to adjust the pH value to 5.8, and the wet gel was obtained by standing at 12°C for 400 min.

[0043] The wet gel was soaked in a TEOS / ethanol solution (volume ratio of TEOS to ethanol was 1:3) at 15°C for 8 d, and then washed in deionized water for 3 times to remove impurity ions in the gel, with each time of soaking for 1.5 d. Finally, the wet gel was soaked in acetone at 15°C for 4 d to replace the water in the wet gel, and the SiO2 wet gel was obtained.

[0044] The F-doped SiO2 aerogel was obtained by freeze-drying the SiO2 wet gel.

[0045] The specific surface area and porosity of the fluorine-containing silica aerogel prepared in this example were 689 m2 / g and 96.6%, respectively, and the dielectric constant at 1000 Hz was 1.34.

[0046] Example 4 The fluorine-containing silicon slag was dispersed in deionized water by stirring, and then dehydrated by vacuum filtration. The dehydrated silicon slag was again dispersed in deionized water, and the dispersion and filtration were repeated for 5 times. Then, the filtered silicon slag was dried in a vacuum oven at 110°C for 60 min, ground into fine powder, and sieved. The fluorine content in the fluorine-containing silicon slag was determined to be 12.46 wt%. The pretreated fluorine-containing silicon slag was stirred and dissolved in 1 mol / L sodium hydroxide aqueous solution, and then the undissolved residue was filtered to obtain a fluorine-containing sodium silicate aqueous solution with a concentration of 20 wt%. The fluorine-containing sodium silicate solution was subjected to sodium removal treatment by using a styrene cation exchange resin to obtain a fluorine-containing silicic acid aqueous solution. 1 mol / L ammonia water was added to adjust the pH value to 5.8, and the wet gel was obtained by standing at 12°C for 400 min.

[0047] The wet gel was immersed in a mixed solution of TEOS, water and ethanol (volume ratio of TEOS, water and ethanol was 1:1:2) at 15°C for 8 days; then the gel was washed in deionized water for 3 times to remove the impurity ions in the gel, each time for 6 hours; finally, the water in the wet gel was replaced by n-hexane by immersing the wet gel in n-hexane at 15°C for 4 days to obtain the SiO2 wet gel.

[0048] The SiO2 wet gel was freeze-dried to obtain the F-doped SiO2 aerogel.

[0049] The specific surface area and porosity of the F-doped SiO2 aerogel prepared in this example were 848 m2 / g and 97.2% respectively, and the dielectric constant at 1000 Hz was 1.22.

[0050] Example 5: The fluorine-containing silicon slag was dried in a vacuum oven at 110°C for 60 minutes to remove the water, and then ground into fine powder and sieved. The fluorine content in the fluorine-containing silicon slag was determined to be 19.86%. The pretreated fluorine-containing silicon slag was dissolved in 1 mol / L sodium hydroxide aqueous solution by stirring, and then the undissolved residue was filtered to obtain a fluorine-containing sodium silicate aqueous solution with a concentration of 20 wt%. Polyvinyl alcohol with a molecular weight of 7000 was dissolved in deionized water by stirring to form a uniform solution with a concentration of 0.05 wt%, and the polyvinyl alcohol aqueous solution was uniformly mixed with the fluorine-containing sodium silicate aqueous solution (the addition amount was 0.5 wt% of the fluorine-containing sodium silicate). 1 mol / L ammonia water was added to adjust the pH value to 5.8, and the mixture was left to react at 12°C for 400 minutes to obtain a wet gel.

[0051] The wet gel was immersed in a TEOS / ethanol solution (volume ratio of TEOS and ethanol was 1:3) at 15°C for 8 days; then the gel was washed in deionized water for 3 times to remove the impurity ions in the gel, each time for 6 hours; finally, the water in the wet gel was replaced by n-hexane by immersing the wet gel in n-hexane at 15°C for 4 days.

[0052] The SiO2 wet gel was freeze-dried to remove the water, and then placed in a muffle furnace for high-temperature calcination at 800°C in an air atmosphere for 6 hours to remove the polymer template. After natural cooling, the F-doped SiO2 aerogel was obtained.

[0053] The specific surface area and porosity of the F-doped SiO2 aerogel prepared in this example were 848 m2 / g and 97.2% respectively, and the dielectric constant at 1000 Hz was 1.22.

[0054] Comparative Example 1: Except that 0.5 mol / L ammonia water was added to adjust the pH value to 4.0, and the mixture was left to react at 5°C for 1200 minutes, the rest was the same as in Example 3. No gel was formed in this example.

[0055] Comparative Example 2: The same procedures as in Example 3 were followed except that 1.5 mol / L ammonia water was added to adjust the pH to 8.0 and the reaction was allowed to proceed at 30° C. for 100 min. In this example, the sol quickly transformed into a hard gel mass and lost its elasticity.

[0056] Comparative Example 3 The wet gel was immersed in a TEOS / ethanol solution (TEOS to ethanol volume ratio of 1:3) at 15° C. for 3 days, as in Example 3. However, the gel was fragile and had insufficient mechanical strength.

[0057] Comparative Example 4 The wet gel was immersed in a TEOS / ethanol solution (TEOS to ethanol volume ratio of 1:3) at 15°C for 12 days, as in Example 3. The surface of the resulting aerogel collapsed, and its specific surface area and porosity were measured to be 230 m2 / g and 74.3%, respectively, and its dielectric constant at 1000 Hz was 2.81.

[0058] Examples and comparative examples:

Claims

1. A method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag, characterized in that: The fluorine-containing silicon slag is dried and ground into fine powder, sieved, and then reacted with sodium hydroxide aqueous solution and filtered to prepare a fluorine-containing sodium silicate solution. A wet gel is prepared by a gel sol method or a template method, and then aged and dried to obtain F-doped SiO2 aerogel. In the aging step, the wet gel is placed in an aging agent solution and soaked at 5-30° C. for 5-10 days, then soaked and washed in deionized water for multiple times to wash out impurity ions in the wet gel, and finally soaked and washed in a displacement solvent to replace water in the wet gel.

2. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 1, characterized in that: The moisture content in the fluorine-containing silicon slag is controlled to be below 2wt% after drying.

3. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 1, characterized in that: The preparation method of the fluorine-containing sodium silicate solution is as follows: the sieved fluorine-containing silicon slag is stirred and dissolved in a sodium hydroxide aqueous solution with a concentration of 1-3 mol / L, and then the undissolved residue is filtered to obtain the fluorine-containing sodium silicate aqueous solution, and the concentration of the fluorine-containing sodium silicate aqueous solution is controlled to be 15-25 wt%.

4. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 1, characterized in that: The sol-gel method comprises the following steps: the sodium silicate solution containing fluorine is subjected to a cation exchange resin for sodium removal to obtain a fluorine-containing silicic acid aqueous solution, an alkaline catalyst is added to adjust the pH value to 4-8, and the solution is allowed to stand for reaction to obtain a wet gel; The template method comprises the following steps: removing sodium from the fluorine-containing sodium silicate solution through a cation exchange resin to obtain a fluorine-containing silicic acid aqueous solution; uniformly mixing the template solution and the fluorine-containing silicic acid aqueous solution; adding an alkaline catalyst to the mixed solution to adjust the pH value to 4-8; and allowing the solution to react to obtain a wet gel.

5. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 4, characterized in that: In the sol-gel method or template method, after adding an alkaline catalyst to adjust the pH value, the mixture is allowed to stand at 5-30° C. for 200-1000 minutes to obtain a wet gel.

6. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 4, characterized in that: The alkaline catalyst is one of ammonia water, NaOH, monoethanolamine, diethanolamine and triethanolamine.

7. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 4, characterized in that: The template is one of polyvinyl alcohol, polymethyl pyrrolidone, polyacrylic acid, polyacrylamide, carboxymethyl cellulose, polyethylene glycol, chitosan, collagen, and starch, with a molecular weight range of 5000-20000, an aqueous solution concentration of 0.02-2wt%, and an addition amount mass ratio of template: sodium fluoride silicate = (0.1-1):

1.

8. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to any one of claims 1 to 7, characterized in that: In the aging step, the wet gel is immersed in deionized water for 1-2 days each time, and immersed in the replacement solvent at a temperature of 5-30° C. for 3-5 days.

9. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to any one of claims 1 to 7, characterized in that: The aging agent solution is ethanol, or a mixed solution of ethanol, TEOS and / or water.

10. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to any one of claims 1 to 7, characterized in that: The replacement solvent is one of methanol, acetone, ethanol, toluene, isopropanol, n-hexane or n-heptane.

11. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 1, characterized in that: The drying method is freeze drying or CO2 supercritical drying.

12. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 1, characterized in that: If the template method is used to prepare the wet gel, a template removal step is added after drying: the SiO2 aerogel obtained after drying is placed in a muffle furnace and calcined at high temperature in an air atmosphere to remove the polymer template, and then naturally cooled to obtain the F-doped SiO2 aerogel.

13. The method for preparing low dielectric fluorine-doped silica aerogel from fluorine-containing silicon slag according to claim 12, characterized in that: The calcination temperature is 500-1000° C., and the calcination time is 2-10 hours.

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