A wet method for preparing high-purity silica and its application

Abstract

This invention provides a wet process for preparing high-purity silica and its application, relating to the fields of inorganic non-metallic material preparation and wet chemical processes. The method includes: alkali dissolving a silicon-containing raw material to obtain a silicate solution, followed by clarification and filtration; immobilizing the silicate solution on an anion exchange solid medium with quaternary ammonium groups under alkaline conditions and separating the mother liquor; subjecting the immobilized medium to displacement washing to remove soluble salts and metal ions; then contacting it with an acidic eluent and controlling acidification in stages to allow controlled condensation of silicic acid to form a silica sol; after aging and gelation, solid-liquid separation, washing, and drying are performed to obtain high-purity silica. This wet process for preparing high-purity silica and its application can reduce impurity entrainment and inhibit uncontrolled nucleation and aggregation, improving product purity and batch stability. The obtained silica, when used as an electronic packaging potting compound, can reduce ion deposition and improve insulation performance.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic material preparation and wet chemical process technology, specifically to a wet preparation method for high-purity silicon dioxide and its application. Background Technology

[0002] Silica, as an important inorganic non-metallic material and functional filler, is widely used in electronic packaging, optical materials, precision chemicals, and composite materials. Existing preparation routes mainly include chemical precipitation, sol-gel methods, gas-phase methods, and wet extraction and conversion based on solid silicon sources or silicon-containing waste. Among these, publicly available technologies have achieved silica preparation through wet systems. For example, silicate resources are converted into soluble silicon components via an alkaline method, followed by acidification and sol-gel to generate silica gel; silicon-based waste is then subjected to wet purification processes such as alcohol washing, acid washing, and water washing to obtain silica products. Some technical solutions can obtain amorphous silica with high purity.

[0003] However, the existing technologies mentioned above still have shortcomings when it comes to achieving high purity: metal ions, salts and fine solid phase impurities are easily introduced or entrained during the wet process, and silicic acid is prone to form colloids and generate uncontrolled nucleation during the conversion from strong alkali to acid, which leads to impurity encapsulation, agglomeration, and difficulty in guaranteeing purity and batch stability. It is difficult to meet the requirements of high-end applications for low metal impurities and controllable particle size and dispersibility. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a wet process for preparing high-purity silica and its application. Through a wet process of immobilization-displacement washing-segmented acidic elution and pH-controlled condensation, high-purity, low-ion silica is prepared and used to improve the insulation performance of electronic packaging potting compounds.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a wet method for preparing high-purity silica, comprising: S1. A silicon-containing raw material is reacted with an alkaline solution to allow the silicon component in the silicon-containing raw material to enter the liquid phase in the form of alkali metal silicates, thereby obtaining a silicate solution with a pH value of 11.0-13.5. S2. The silicate solution is subjected to solid-liquid separation, and the separated silicate solution is micro-filtered to remove insoluble matter and fine solid phase impurities to obtain a clear silicate solution; S3. Under the condition that the pH value of the clarified silicate solution is maintained at 10.5-13.5, the clarified silicate solution is brought into contact with the solid support medium, so that the silicate in the clarified silicate solution is immobilized by the solid support medium in the form of anions, and the solid support medium immobilized with silicate is separated from the unimmobilized mother liquor. The solid support medium is an anion exchange type solid phase medium with quaternary ammonium groups. S4. Perform at least one displacement washing on the silicate-supported medium, wherein the displacement washing medium is an alkaline washing solution, so that soluble salts and metal ions are discharged with the alkaline washing solution, wherein the conductivity of the alkaline washing solution is not higher than 5000 μS / cm. S5. The immobilized medium after the displacement washing is contacted with an acidic eluent, the conductivity of which is not higher than 3000 μS / cm, so that the silicate immobilized on the immobilized medium is released into the acidic eluent and acidified into silicic acid. The pH value of the acidic eluent is controlled to gradually decrease to 4.0-6.0, so that the silicic acid is controlled to condense to form a silica sol. The silica sol is then aged and gelled to form a wet gel. The wet gel is subjected to solid-liquid separation, washing, and drying to obtain a high-purity silica product.

[0006] Preferably, the alkaline solution is an alkali metal hydroxide solution or an alkali metal carbonate solution.

[0007] Preferably, the pore size of the filter medium in the microfiltration is 0.05μm-1.0μm.

[0008] Preferably, the supporting medium is an anion exchange resin with quaternary ammonium groups, and the average particle size of the anion exchange resin is 0.2 mm to 1.2 mm.

[0009] Preferably, the clarified silicate solution is contacted with the solidification medium by either column dynamic exchange or stirred batch contact. In column dynamic exchange, the solidification completion criterion is that the change in silicon content in the effluent does not exceed ±5% within 30 minutes. In stirred batch contact, the solidification completion criterion is that the change in silicon content in the mother liquor does not exceed ±5% within 30 minutes. The silicon content is expressed as SiO2 equivalent content.

[0010] Preferably, the number of replacement washes is 2 to 6 times, and the endpoint of the last replacement wash is that the absolute value of the difference between the conductivity of the wash effluent and the conductivity of the alkaline wash solution is not greater than 1000 μS / cm, and the pH value of the alkaline wash solution is 10.5-13.5.

[0011] Preferably, the conductivity of the alkaline washing solution is not higher than 3000 μS / cm.

[0012] Preferably, the acidic eluent is an aqueous solution of an inorganic acid, wherein the inorganic acid is any one or more of hydrochloric acid, nitric acid, or sulfuric acid.

[0013] Preferably, the gradual reduction is implemented using a segmented control method, which includes the following steps: S51. First stage: Adjust the pH value of the acidic eluent to 6.0-8.0, with pH fluctuation not exceeding ±0.2, and continue for 5min-30min before proceeding to the second stage; S52. Second stage: Adjust the pH value of the acidic eluent to 4.0-6.0, and the segmented adjustment is achieved by adding acidic components.

[0014] An application of high-purity silica includes: adding the high-purity silica to an electronic packaging potting compound system and dispersing and mixing it to obtain a potting compound composition for electronic packaging, wherein the conductivity of the water extract of the high-purity silica is not higher than 500 μS / cm, and the volume resistivity of the potting compound composition at 25°C is not lower than 1×10^14 Ω·cm.

[0015] This invention provides a wet method for preparing high-purity silica and its application. It has the following beneficial effects: This wet process for preparing high-purity silica and its application employs a coupled process: alkali dissolution—clarification microfiltration—quaternary ammonium anion exchange immobilization—low-conductivity alkali washing and displacement—low-conductivity acid washing with segmented pH release and controlled condensation to form a gel. Silicates are first immobilized on a solid medium and subjected to displacement washing in an alkaline, low-salt environment. Then, under low-conductivity acidic elution conditions, pH is controlled in stages to achieve controlled condensation. This effectively reduces the entrainment and introduction of metal ions, salts, and fine solid-phase impurities during the wet process, inhibits uncontrolled nucleation and aggregation caused by localized supersaturation during the conversion from strong alkali to acid, thereby improving product purity and batch stability. Furthermore, the process is controllable and repeatable through conductivity difference endpoint criteria and segmented pH control.

[0016] The high-purity silica obtained by this invention has the characteristic of low soluble ion precipitation. When used in electronic packaging potting compound systems, it can significantly reduce the adverse effects of ion migration and impurity ions on insulation performance, so that the volume resistivity of the potting compound composition at 25°C is not less than 1×10^14 Ω·cm, thereby meeting the requirements of high insulation reliability for electronic packaging and providing support for the long-term stable operation of potting compound materials. Attached Figure Description

[0017] Figure 1 A flowchart of a wet process for preparing high-purity silica; Figure 2 This is a block diagram of the control logic for fixed loading, displacement washing, and segmented elution acidification. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0019] like Figure 1-2 As shown, this embodiment of the invention provides a wet method for preparing high-purity silica, comprising: raw materials and reagents: Silicon-containing raw materials: silicon micro powder, SiO2 mass fraction ≥99.5%, D50≈10μm.

[0020] Alkaline solution: NaOH aqueous solution, mass fraction 20wt%, solid-liquid ratio approximately 1:5 g:mL.

[0021] Immobilized medium: anion exchange resin with quaternary ammonium groups, with an average particle size of 0.6 mm. It is pre-washed with deionized water before use until the conductivity of the effluent is stable.

[0022] Microfiltration media: 0.20μm microfiltration membrane.

[0023] Acidic eluent: prepared with deionized water, with an initial conductivity of approximately 50 μS / cm. pH segmentation is achieved by adding 0.1 mol / L hydrochloric acid as the acidic component during segmented control.

[0024] Conductivity measurement: All measurements were performed using a conductivity meter at 25℃.

[0025] S1. The silicon micropowder is reacted with an alkaline solution, so that the silicon component in the silicon micropowder enters the liquid phase in the form of alkali metal silicates, and a silicate solution is obtained. The pH value of the silicate solution is 11.0-13.5.

[0026] Specifically: Weigh 500g of silica powder, add 2500mL of NaOH solution, and react at 85℃ with mechanical stirring for 3h. During the reaction, monitor the pH with a pH meter. If the pH is lower than 11.0, add a small amount of NaOH solution. If the pH is higher than 13.5, add deionized water to adjust the pH so that the pH of the system is maintained within the range of 12.5±0.5, and a silicate solution is obtained.

[0027] S2. Solid-liquid separation is performed on the silicate solution, and the separated silicate solution is microfiltered to remove insoluble matter and fine solid phase impurities to obtain a clear silicate solution. The pore size of the microfiltration medium is 0.20 μm.

[0028] Specifically: After the reaction solution is cooled to room temperature, it is centrifuged at 6000 rpm for 10 minutes to remove insoluble residues. The supernatant is then filtered through a 0.20 μm microfiltration membrane to obtain a clear silicate solution.

[0029] S3. Under the condition that the pH of the clarified silicate solution is maintained at 10.5–13.5, the clarified silicate solution is brought into contact with a supporting medium, so that the silicates in the clarified silicate solution are immobilized in the form of anions by the supporting medium. The supporting medium with immobilized silicates is then separated from the unimmobilized mother liquor. The supporting medium is an anion exchange solid-phase medium with quaternary ammonium groups, and the average particle size of the anion exchange resin is 0.6 mm. The contact method between the clarified silicate solution and the supporting medium is column dynamic exchange. During column dynamic exchange, the immobilization is considered complete when the change in silicon content in the effluent does not exceed ±5% within 30 minutes. The silicon content is expressed as SiO2 equivalent content.

[0030] Specifically: Anion exchange resin was packed into an exchange column with a wet volume of 500 mL (1 BV). A clear silicate solution was passed through the resin bed at a flow rate of 3 BV / h. During the process, the pH of the effluent was monitored, and a small amount of NaOH solution was added to maintain the pH between 11.5 and 13.0. Samples were taken every 10 minutes to determine the silicon content in the effluent. The immobilization was considered complete when the SiO2 equivalent content in the effluent did not change by more than ±5% within 30 minutes. In this example, the SiO2 equivalent content in the effluent at the end of the immobilization was approximately 2.0 g / L, with a change of ≤ ±5% within 30 minutes.

[0031] S4. Perform at least one displacement wash on the silicate-supported medium. The displacement wash medium is an alkaline washing solution, which removes soluble salts and metal ions with the alkaline washing solution. The conductivity of the alkaline washing solution is not higher than 5000 μS / cm. The displacement wash is performed 4 times. The endpoint of the last displacement wash is when the absolute value of the difference between the conductivity of the washing solution and the conductivity of the alkaline washing solution is not greater than 1000 μS / cm. The pH value of the alkaline washing solution is 10.5-13.5.

[0032] Specifically: The alkaline washing solution was prepared as a 0.01 mol / L NaOH aqueous solution with a pH of approximately 12.0 and a conductivity of approximately 2300 μS / cm at 25°C. The resin was washed four times with this alkaline washing solution, with a washing solution volume of 1 BV each time. The conductivity of the washing solution was measured. In this embodiment, the conductivity of the last washing solution was approximately 2800 μS / cm, and the absolute value of the difference between the conductivity of the washing solution and the conductivity of the washing solution was approximately 500 μS / cm, which met the endpoint criterion.

[0033] S5. The immobilized medium after displacement washing is contacted with an acidic eluent with a conductivity not exceeding 3000 μS / cm. This releases the silicates immobilized on the medium into the acidic eluent, where they are acidified into silicic acid. The pH of the acidic eluent is gradually reduced to 4.0-6.0, allowing the silicic acid to undergo controlled condensation to form a silica sol. The silica sol is then aged and gelled to form a wet gel. The wet gel is subjected to solid-liquid separation, washing, and drying to obtain a high-purity silica product. The acidic eluent is an aqueous solution of an inorganic acid, which is any one or more of hydrochloric acid, nitric acid, or sulfuric acid.

[0034] The approach will be gradually reduced to a segmented control method, including the following steps: S51. First stage: Adjust the pH of the acidic eluent to 6.0-8.0, with pH fluctuation not exceeding ±0.2, and continue for 5-30 minutes before entering the second stage.

[0035] S52. Second stage: Adjust the pH of the acidic eluent to 4.0-6.0, which is achieved by adding acidic components in stages.

[0036] Specifically: The resin was subjected to column elution using deionized water as the eluent, with an initial conductivity of approximately 50 μS / cm. pH was monitored online, and 0.1 mol / L hydrochloric acid was added dropwise as an acidic component for segmented elution. Simultaneously, the conductivity of the eluent was monitored and controlled to ≤3000 μS / cm. The segmented elution control was as follows: First stage: Adjust the pH of the eluent to 7.0, with fluctuations not exceeding ±0.2, and continue for 15 minutes before proceeding to the second stage.

[0037] Second stage: Continue to add hydrochloric acid to bring the pH of the eluent to 5.0, and obtain silica sol.

[0038] The obtained silica sol was placed at 25°C and allowed to stand for 12 hours to age, gelling to form a wet gel. The wet gel was then obtained by solid-liquid separation using vacuum filtration.

[0039] Endpoint criteria for wet gel washing: The wet gel was washed 6 times with deionized water at a solid-liquid ratio of approximately 1:10 g:mL each time, using any one or a combination of the following criteria as the washing endpoint: 1) The conductivity of the washing liquid at 25℃ is ≤200μS / cm.

[0040] 2) Ion chromatography was used to determine the Cl content in the washing effluent. - ≤5mg / L, SO4 2- ≤5mg / L, NO3 - ≤5mg / L.

[0041] In this embodiment, the final conductivity of the washing effluent is approximately 150 μS / cm, and Cl - SO4 2- / NO3 - All values ​​were ≤5 mg / L, meeting the endpoint criterion.

[0042] Drying: The washed wet gel was vacuum dried at 80℃ for 12 hours to obtain high-purity silica powder.

[0043] Test results: Conductivity of water extract: 10g of silica sample was extracted with 200mL of deionized water at 25℃ for 2h with stirring. After filtration through 0.45μm, the conductivity was measured, and the result was 320μS / cm. Metallic impurities: Fe 1.2ppm, Al 2.5ppm, Ca 1.0ppm, Mg 0.5ppm, Na 3.0ppm, K 0.8ppm, total metallic impurities approximately 9.0ppm, SiO2 content 99.95wt%.

[0044] An application of high-purity silica in electronic packaging potting compound includes: adding high-purity silica to an electronic packaging potting compound system and dispersing and mixing it to obtain a potting compound composition for electronic packaging, wherein the conductivity of the water extract of high-purity silica is not higher than 500 μS / cm, and the volume resistivity of the potting compound composition at 25°C is not lower than 1×10^14 Ω·cm.

[0045] Specifically: Formulation and dispersion: Add silica at 40 wt% of the total mass of the potting compound system, disperse using a planetary mixer degasser at 1000 rpm for 10 min, and then perform vacuum degassing at -0.09 MPa for 5 min.

[0046] Curing conditions: Pour the mixture into a board with a thickness of about 2 mm and cure at 120℃ for 1 hour.

[0047] Volume resistivity test: A voltage of 500V was applied at 25℃ and held for 60s. The volume resistivity was measured to be 3.0×10^14Ω·cm. Example 2

[0048] Based on Example 1, the alkaline solution in step S1 is replaced with an alkali metal carbonate solution instead of NaOH solution, and the remaining steps S2-S5 are the same as in Example 1.

[0049] Specifically: 500g of silica powder was weighed and added to 2500mL of a 20wt% Na2CO3 aqueous solution. The mixture was reacted at 85℃ and 300rpm for 3 hours. During the reaction, Na2CO3 solution or deionized water was added to adjust the pH of the system to 11.0-13.5 to obtain a silicate solution. Subsequently, solid-liquid separation and 0.20μm microfiltration were performed according to Example 1 to obtain a clear silicate solution. The silicate was immobilized on a quaternary ammonium anion exchange resin using a column dynamic exchange method while maintaining the pH at 10.5-13.5. The solution was washed according to Example 1, and then acidic eluent with a conductivity ≤3000μS / cm was used for segmented acid addition to obtain silica sol. The sol was then aged and gelled to form a wet gel. The wet gel was washed to the endpoint criterion and then dried to obtain the silica product.

[0050] Test results: The obtained silica powder has a SiO2 content of 99.92wt% and a total metal impurity content of ≤12ppm. The conductivity of the water extract was measured to be 380μS / cm under the extraction conditions of Example 1. Example 3

[0051] Based on Example 1, the fixation method in step S3 is changed from column dynamic exchange to stirring batch contact, and the remaining steps S1, S2, S4 and S5 are the same as in Example 1.

[0052] Specifically: The clarified silicate solution obtained in step S2 was mixed with anion exchange resin containing quaternary ammonium groups at a resin wet volume: solution volume ratio of 1:10. The mixture was stirred at 300 rpm for 2 hours at room temperature. During the contact process, samples were taken intermittently to determine the silicon content in the mother liquor. The immobilization was considered complete when the SiO2 equivalent content in the mother liquor did not change by more than ±5% within 30 minutes. Subsequently, the silicate-immobilized resin was separated from the mother liquor by filtration. The separated resin was subjected to displacement washing as described in Example 1, followed by acid elution, segmented pH adjustment, aging gelation, wet gel washing, and drying as described in Example 1 to obtain the silica product.

[0053] Test results: The obtained silica powder has a SiO2 content of 99.94 wt% and a total metal impurity content of ≤11 ppm. The conductivity of the water extract was measured to be 340 μS / cm under the extraction conditions of Example 1. Example 4

[0054] Based on Example 1, the acidic component in step S5 was replaced with 0.1 mol / L hydrochloric acid, and the operating conditions in the remaining steps S1-S4 and S5, except for the acidic component, were the same as in Example 1.

[0055] Specifically: the acidic eluent still uses deionized water as the base solution, and the pH is controlled in stages by adding 0.1 mol / L nitric acid dropwise in stages through online pH monitoring; in the first stage, the pH is controlled at 6.0-8.0 and maintained (fluctuation ≤ ±0.2) for 15 min before entering the second stage, where the pH is controlled at 4.0-6.0 to obtain silica sol. The conductivity of the system is always controlled at ≤3000 μS / cm during the elution process. Subsequently, the gel is aged and gelled according to the conditions of Example 1 to form a wet gel, and washed and dried according to the wet gel washing endpoint criteria of Example 1 to obtain the silica product.

[0056] Test results: The obtained silica powder had a SiO2 content of 99.93 wt%; the total amount of metal impurities was ≤10 ppm; the conductivity of the water extract was 300 μS / cm under the extraction conditions of Example 1; and the NO3 content in the final washing effluent was determined by ion chromatography. - Cl - SO4 2- The content of all samples is ≤5mg / L. Example 5

[0057] Based on Example 1, the conductivity control in steps S4 and S5 was adjusted to near the upper limit, with the conductivity of the alkaline washing solution ≤5000μS / cm and the conductivity of the acidic eluent ≤3000μS / cm. The microfiltration in step S2 was changed to use a microfiltration membrane with a pore size of 0.90μm, and the average particle size of the anion exchange resin used in step S3 was adjusted to 1.00mm. All other operating conditions were the same as in Example 1.

[0058] Specifically: Step S4 Displacement Washing: The alkaline washing solution was replaced with a 0.02 mol / L NaOH aqueous solution with a pH of approximately 13.0 and a conductivity of approximately 4800 μS / cm at 25°C. The alkaline washing solution was used for displacement washing twice, with a volume of 1 BV each time. In this embodiment, the conductivity of the final wash effluent was approximately 5200 μS / cm, and the absolute value of the difference between the conductivity of the final wash effluent and that of the washing solution was approximately 400 μS / cm, which met the endpoint criterion.

[0059] Step S5: Acidic Elution and Segmented Control: The acidic eluent still uses deionized water as the base solution. 0.1 mol / L hydrochloric acid is added dropwise as an acidic component through online pH monitoring to achieve segmented control. At the same time, the conductivity of the elution system is controlled in the range of 2500-2950 μS / cm and always ≤3000 μS / cm through online conductivity monitoring. In the first stage, the pH is adjusted to 6.0-8.0 and maintained (fluctuation ≤±0.2) for 10 min before entering the second stage. In the second stage, the pH is adjusted to 4.0-6.0 to obtain silica sol. Subsequently, it is aged and gelled according to the conditions of Example 1 to form a wet gel. The wet gel is washed and dried according to the washing endpoint criteria of Example 1 to obtain the silica product.

[0060] Test results: The SiO2 content of the obtained silica powder was 99.90 wt%; the total amount of metal impurities was ≤12 ppm; and the conductivity of the water extract was 480 μS / cm, measured under the extraction conditions of Example 1. Example 6

[0061] Based on Example 1, a preferred scheme with an alkaline washing solution conductivity ≤3000μS / cm was adopted, and the residual soluble ions were further reduced. The conductivity of the alkaline washing solution in step S4 was controlled at a low level, and the conductivity of the elution process in step S5 was also controlled in a low range. The microfiltration in step S2 was changed to use a microfiltration membrane with a pore size of 0.06μm, and the average particle size of the anion exchange resin used in step S3 was adjusted to 0.30mm. All other operating conditions were the same as in Example 1.

[0062] Specifically: Step S4 Displacement Washing: The alkaline washing solution was replaced with a 0.005 mol / L NaOH aqueous solution with a pH of approximately 11.7 and a conductivity of approximately 1200 μS / cm at 25°C. The alkaline washing solution was used for displacement washing 6 times, with a volume of 1 BV each time. In this embodiment, the conductivity of the final wash effluent was approximately 1700 μS / cm, and the absolute value of the difference between the conductivity of the final wash effluent and that of the washing solution was approximately 500 μS / cm, which met the endpoint criterion.

[0063] Step S5: Acidic elution and segmented control: The acidic eluent uses deionized water as the base solution. 0.1 mol / L hydrochloric acid is added dropwise as an acidic component through online pH monitoring to achieve segmented control. At the same time, the conductivity of the elution system is controlled in the range of 200-1200 μS / cm and is always ≤3000 μS / cm. In the first stage, the pH is controlled at 6.0-8.0 and maintained (fluctuation ≤±0.2) for 20 min before entering the second stage. In the second stage, the pH is controlled at 4.0-6.0 to obtain silica sol. Subsequently, it is aged and gelled according to the conditions of Example 1 to form a wet gel. The wet gel is washed and dried according to the washing endpoint criteria of Example 1 to obtain the silica product.

[0064] Test results: The SiO2 content of the obtained silica powder was 99.96 wt%; the total amount of metal impurities was ≤8 ppm; and the conductivity of the water extract was 180 μS / cm, measured under the extraction conditions of Example 1. Example 7

[0065] This embodiment is an application embodiment, which uses the high-purity silica obtained in Example 6 as a filler to prepare an electronic packaging potting compound composition and test its insulation performance.

[0066] 1) Conductivity of silica aqueous extract Take 10g of the silica sample obtained in Example 6, add 200mL of deionized water with a solid-liquid ratio of 1:20g:mL, and extract with magnetic stirring at 25℃ for 2h. After filtration through a 0.45μm filter membrane at 25℃, measure the conductivity of the filtrate. The conductivity of the water extract is 180μS / cm.

[0067] 2) Preparation of potting compound composition A two-component system of silicone potting compound (components A and B, which can be cured at room temperature or by heating) was selected. The silica from Example 6 was added to component A at 40 wt% of the total mass of the potting compound system. The mixture was dispersed for 10 min using a planetary mixer and degassed under vacuum for 5 min. Then, component B was added according to the manufacturer's recommended ratio and stirred for 3 min. The mixture was then degassed under vacuum again for 3 min to obtain the potting compound composition, which was then potted and molded.

[0068] 3) Curing and Sample Preparation The potting compound composition was poured into a mold to prepare a plate-shaped sample with a thickness of about 2 mm. After curing at 120°C for 1 hour, it was placed at 25°C for 24 hours to complete the curing process.

[0069] 4) Volume resistivity test The volume resistivity was tested at 25℃ according to the GB / T1410 method: using parallel plate electrodes, a DC voltage of 500V was applied, and the voltage was held for 60s. The volume resistivity of the potting compound was measured to be 3.0×10^14Ω·cm. Example 8

[0070] This embodiment is a comparative embodiment. In order to verify the insulation improvement effect of the high-purity silica of the present invention in electronic packaging potting compound, commercially available ordinary silica (not processed by the immobilization-displacement washing-segmented elution process of the present invention) was selected as filler, and potting compound composition was prepared and tested under the same potting compound system and the same process conditions.

[0071] 1) Comparison of the conductivity of silica water extract Take 10g of commercially available ordinary silica sample, add 200mL of deionized water with a solid-liquid ratio of 1:20g:mL, stir and extract at 25℃ for 2h, and then filter through a 0.45μm filter membrane at 25℃ to measure the conductivity of the filtrate. The conductivity of the water extract is 1200μS / cm.

[0072] 2) Comparison of potting compound composition preparation and curing Using the same two-component silicone potting compound system as in Example 7, commercially available ordinary silica was added to component A at 40 wt% of the total mass of the potting compound system. The mixture was dispersed for 10 min using a planetary mixer and degassed under vacuum for 5 min. Then, component B was added in the same proportion and stirred for 3 min. The mixture was then degassed under vacuum again for 3 min to obtain the comparative potting compound composition, which was then cast into shape.

[0073] The sample was prepared as a plate-shaped specimen with a thickness of about 2 mm, cured at 120℃ for 1 h, and then placed at 25℃ for 24 h.

[0074] 3) Volume resistivity test The volume resistivity was tested at 25℃ according to the GB / T1410 method. The volume resistivity of the comparative potting compound was 6.0×10^13Ω·cm, which is lower than 1×10^14Ω·cm.

[0075] Comparative conclusion: Compared with Example 7, the silica water extract used in this comparative example has a significantly higher conductivity, resulting in a decrease in the volume resistivity of the potting compound composition. This indicates that the low-ion high-purity silica prepared by the method of the present invention can effectively improve the insulation performance of electronic packaging potting compounds.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A wet method for preparing high-purity silica, characterized in that, include: S1. A silicon-containing raw material is reacted with an alkaline solution to allow the silicon component in the silicon-containing raw material to enter the liquid phase in the form of alkali metal silicates, thereby obtaining a silicate solution with a pH value of 11.0-13.

5. S2. Perform solid-liquid separation on the silicate solution, and then perform microfiltration on the separated silicate solution to obtain a clear silicate solution; S3. Under the condition that the pH value of the clarified silicate solution is maintained at 10.5-13.5, the clarified silicate solution is brought into contact with the solid support medium, so that the silicate in the clarified silicate solution is immobilized by the solid support medium in the form of anions, and the solid support medium immobilized with silicate is separated from the unimmobilized mother liquor. The solid support medium is an anion exchange type solid phase medium with quaternary ammonium groups. S4. Perform at least one displacement washing on the silicate-supported medium, wherein the displacement washing medium is an alkaline washing solution, so that soluble salts and metal ions are discharged with the alkaline washing solution, wherein the conductivity of the alkaline washing solution is not higher than 5000 μS / cm. S5. The immobilized medium after the displacement washing is contacted with an acidic eluent, the conductivity of which is not higher than 3000 μS / cm, so that the silicate immobilized on the immobilized medium is released into the acidic eluent and acidified into silicic acid. The pH value of the acidic eluent is controlled to gradually decrease to 4.0-6.0, so that the silicic acid is controlled to condense to form a silica sol. The silica sol is then aged and gelled to form a wet gel. The wet gel is subjected to solid-liquid separation, washing, and drying to obtain a high-purity silica product.

2. The wet preparation method of high-purity silica according to claim 1, characterized in that: The alkaline solution is an alkali metal hydroxide solution or an alkali metal carbonate solution.

3. The wet preparation method of high-purity silica according to claim 1, characterized in that: The pore size of the filter medium in the microfiltration is 0.05μm-1.0μm.

4. The wet preparation method of high-purity silica according to claim 1, characterized in that: The supporting medium is an anion exchange resin with quaternary ammonium groups, and the average particle size of the anion exchange resin is 0.2 mm to 1.2 mm.

5. The wet preparation method of high-purity silica according to claim 1, characterized in that: The clarified silicate solution is contacted with the solidification medium by either column dynamic exchange or stirred batch contact. In the column dynamic exchange, the solidification completion criterion is that the change in silicon content in the effluent does not exceed ±5% within 30 minutes. In the stirred batch contact, the solidification completion criterion is that the change in silicon content in the mother liquor does not exceed ±5% within 30 minutes. The silicon content is expressed as SiO2 equivalent content.

6. The wet preparation method of high-purity silica according to claim 1, characterized in that: The number of replacement washes is 2 to 6 times, and the endpoint of the last replacement wash is that the absolute value of the difference between the conductivity of the wash effluent and the conductivity of the alkaline wash solution is not greater than 1000 μS / cm, and the pH value of the alkaline wash solution is 10.5-13.

5.

7. The wet preparation method of high-purity silica according to claim 6, characterized in that: The conductivity of the alkaline washing solution is not higher than 3000 μS / cm.

8. The wet preparation method of high-purity silica according to claim 1, characterized in that: The acidic eluent is an aqueous solution of an inorganic acid, which is any one or more of hydrochloric acid, nitric acid, or sulfuric acid.

9. The wet preparation method of high-purity silica according to claim 1, characterized in that: The gradual reduction to a segmented control method includes the following steps: S51. First stage: Adjust the pH value of the acidic eluent to 6.0-8.0, with pH fluctuation not exceeding ±0.2, and continue for 5min-30min before proceeding to the second stage; S52. Second stage: Adjust the pH value of the acidic eluent to 4.0-6.0, and the segmented adjustment is achieved by adding acidic components.

10. The application of high-purity silica prepared according to any one of claims 1-8 in electronic packaging potting compound, characterized in that, include: The high-purity silica is added to the electronic packaging potting compound system and dispersed and mixed to obtain an electronic packaging potting compound composition. The water extract of the high-purity silica has a conductivity of not more than 500 μS / cm, and the volume resistivity of the potting compound composition at 25°C is not less than 1×10^14 Ω·cm.

Images