A method for preparing high-purity silicon dioxide based on trimethoxysilane precursor

Abstract

The application discloses a method for preparing high-purity silicon dioxide based on trimethoxysilane precursor, and relates to the technical field of high-purity inorganic non-metallic material preparation. The method comprises the following steps: firstly, taking trimethoxysilane as a silicon source, and performing hydrolysis and polycondensation reaction under acid catalysis to form an organic silicon resin precursor; then, through aging, dealcoholization, low-temperature crosslinking and gradient calcination processes, the organic groups are gradually removed and the silicon-oxygen network is densified, and finally high-purity silicon dioxide powder is obtained. By controlling the hydrolysis pH value, alcohol-water ratio, resin crosslinking density and staged temperature rising system, the carbon residue and metal ion impurity content are effectively reduced, the purity of the obtained silicon dioxide can reach more than 99.99%, and the obtained silicon dioxide has the characteristics of narrow particle size distribution, high specific surface area, low hydroxyl residue and excellent thermal stability, and is suitable for the fields of semiconductor packaging materials, electronic paste, quartz crucible auxiliary materials and high-end silicon-based functional materials.

Description

Technical Field

[0001] This invention relates to the field of high-purity inorganic non-metallic material preparation technology, and in particular to a method for preparing high-purity silicon dioxide based on trimethoxysilane precursor. Background Technology

[0002] Silica (SiO2), as an important inorganic non-metallic functional material, is widely used in semiconductor packaging, electronic pastes, CMP polishing materials, optical glass, quartz products, silicone rubber reinforcing materials, and new energy batteries due to its excellent heat resistance, electrical insulation, chemical stability, low coefficient of thermal expansion, and good dielectric properties. Especially in high-end electronic packaging and semiconductor manufacturing, extremely high requirements are placed on the purity, particle size uniformity, hydroxyl content, and metal ion impurity content of silica materials. Typically, SiO2 purity must reach above 99.99%, while metal impurities such as Na, K, Fe, and Ca must be controlled below the ppm level.

[0003] Currently, the main industrial preparation routes for high-purity silica include natural quartz purification, water glass precipitation, silicon tetrachloride vapor-phase oxidation, and organosilicon precursor pyrolysis.

[0004] The natural quartz purification method mainly removes metallic impurities from the ore through acid washing, high-temperature chlorination and flotation. However, due to the complex distribution of impurities in natural quartz ore, especially the fact that elements such as Fe, Al and Ti are easy to exist in the form of lattice doping, it is difficult to remove them completely. At the same time, it also has the problems of long process flow, high acid consumption and heavy environmental burden.

[0005] Although the water glass precipitation method is relatively simple, the raw water glass usually contains a high content of alkali metal ions such as Na⁺ and K⁺, which are easy to remain inside the SiO2 particles during the subsequent precipitation process, making it difficult for the obtained product to meet the requirements of high purity for electronic applications.

[0006] Although the gas-phase oxidation of silicon tetrachloride can produce high-purity spherical SiO2, this method usually requires high-temperature flame hydrolysis equipment, which consumes a lot of energy, has stringent requirements for the corrosion resistance of the equipment, and the treatment of chloride by-products is complicated, resulting in high production costs. Therefore, it limits its application in large-scale, low-cost fields.

[0007] In recent years, the pyrolysis route of organosilicon precursors has gradually become an important development direction for high-purity SiO2 due to its advantages such as good molecular-level uniformity, fewer impurity sources, and controllable structure. The Si-OR groups in organosilicones can undergo controlled hydrolysis and condensation reactions to form a uniform Si-O-Si three-dimensional network structure, which is then converted into high-purity silicon dioxide after thermal decomposition and high-temperature calcination.

[0008] In the prior art, some patents have disclosed methods for preparing organosilicon resins and siloxane materials. For example, patent CN105906810A discloses a method for preparing organopolysiloxane resin, which promotes silane polycondensation reaction by acid catalysis to improve resin uniformity.

[0009] Patent CN104884461B discloses an organopolysiloxane composition containing an alkoxysilane structure, which focuses on improving the molding performance and crosslinking stability of organosilicon materials.

[0010] In addition, in the field of silane coupling agents and trimethoxysilane derivatives, there are literature reports that trimethoxysilanes have high hydrolytic activity, and can be hydrolyzed through Si-OCH3 bonds to generate silanols, which can then be further condensed to form a silicon-oxygen network structure.

[0011] However, existing technologies for preparing SiO2 by pyrolysis of organosilicon precursors still have the following problems:

[0012] (1) The hydrolysis-condensation process is difficult to control precisely.

[0013] Trimethoxysilane compounds have a fast hydrolysis rate. Under conditions of high local water concentration or large pH fluctuations, they are prone to instantaneous gelation, resulting in an uneven resin structure and affecting the subsequent pyrolysis purification effect.

[0014] (2) Organic residual carbon is difficult to completely remove.

[0015] In existing technologies, organosilicon resins are often treated by a one-time high-temperature calcination method, which can easily cause the organic groups to rapidly decompose and carbonize in a short time, forming a closed carbon residual structure. This results in a high residual carbon content in the final product, which in turn affects the purity and dielectric properties of SiO2.

[0016] (3) Particles are prone to agglomeration during calcination.

[0017] When silicone resin softens and shrinks at high temperatures, improper heating rate control can easily lead to particle sintering and agglomeration, resulting in increased silica particle size and decreased specific surface area, making it difficult to meet the application requirements of electronic-grade ultrafine SiO2.

[0018] (4) It is difficult to control metallic impurities.

[0019] The catalysts, containers, and inorganic additives used in some existing processes can easily introduce impurity ions such as Na, Fe, and Ca. At the same time, uneven cross-linking of the resin structure can also cause local enrichment of impurities, affecting the purity of the final product.

[0020] (5) Insufficient process stability and adaptability to large-scale production.

[0021] Some existing technologies rely on complex vacuum equipment or high-temperature gas-phase reaction devices, resulting in a narrow process window and making it difficult to simultaneously meet the demands for high purity, low cost, and continuous production. Summary of the Invention

[0022] Based on the problems raised in the background art, the present invention proposes a method for preparing high-purity silicon dioxide based on trimethoxysilane precursor.

[0023] The technical solution is as follows:

[0024] A method for preparing high-purity silica based on a trimethoxysilane precursor includes the following steps:

[0025] (1) Precursor hydrolysis steps

[0026] According to the mass fraction, 100-140 parts of trimethoxysilane were added to 180-260 parts of anhydrous alcohol solvent, and stirred at 20-35°C to form a homogeneous system; then 18-42 parts of deionized water and 0.3-2.0 parts of acidic catalyst were pre-mixed to form a hydrolysate, which was slowly added dropwise to the homogeneous system over 0.5-2 hours, controlling the pH of the system to be 2.5-4.5, and the reaction was continued for 1-4 hours to obtain a silanol hydrolysate;

[0027] (2) Polycondensation into resin step

[0028] The silanol hydrolysate obtained in step (1) is heated to 45-75°C for polycondensation reaction for 3-10 hours to gradually form an organosilicon resin sol. Then, 0.5-6 parts of complexing stabilizer are added and the reaction is continued for 0.5-3 hours to obtain a transparent or semi-transparent organosilicon resin precursor solution. The solid content of the system is controlled to be 28-45 wt% during the polycondensation process.

[0029] (3) Resin drying and crosslinking steps

[0030] The organosilicon resin precursor liquid obtained in step (2) is subjected to de-alcoholization under reduced pressure at 50-90℃ for 0.5-3h, and then dried at 80-160℃ to allow the organosilicon resin to undergo further cross-linking and curing, thereby obtaining solid organosilicon resin; the reduced pressure is controlled at -0.04 to -0.09MPa.

[0031] (4) Low-temperature pre-pyrolysis step

[0032] The solid organosilicon resin obtained in step (3) is placed in an air atmosphere or a mixed atmosphere with an oxygen content of 5-30 vol%, and heated to 180-350°C at 1-3°C / min and held for 1-4 hours to remove low-boiling organic groups and residual methoxy groups; then the temperature is further increased to 350-650°C at 1-5°C / min and held for 1-5 hours to cause the organic side chains to crack and carbonize.

[0033] (5) High-temperature calcination purification step

[0034] The pre-pyrolyzed product is placed in an air atmosphere, an oxygen atmosphere, or an inert / oxygen mixed atmosphere, heated to 850-1250℃ at a rate of 2-6℃ / min and held at that temperature. After cooling, high-purity silica powder is obtained.

[0035] As a preferred embodiment of the present invention, the trimethoxysilane is one or a combination of two or more of methyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, and hydrotrimethoxysilane.

[0036] As a preferred embodiment of the present invention, the alcohol solvent is one or more of methanol, ethanol, isopropanol, and n-butanol, and the water content in the alcohol solvent is ≤0.2wt%.

[0037] As a preferred embodiment of the present invention, the acidic catalyst is one or more of hydrochloric acid, nitric acid, formic acid, acetic acid, or oxalic acid.

[0038] As a preferred technical solution of the present invention, the stirring speed is controlled to be 350-600 rpm when adding hydrolysate in step (1).

[0039] As a preferred embodiment of the present invention, the preparation method of the complexing stabilizer in step (2) is as follows:

[0040] According to the mass fractions, 25-35 parts of trimethylsilyl methacrylate (CAS: 13688-56-7), 65-75 parts of 2,3-dimercaptosuccinic acid (CAS: 304-55-2), and 350-450 parts of anhydrous dichloroethane were added to a reaction vessel. Nitrogen gas was introduced to remove oxygen for 35-50 minutes. Then, 0.1-0.4 parts of azobisisobutyronitrile (AIBN) were added, and the temperature was raised to 70-80℃ for 2-4 hours. Under 365nm ultraviolet light irradiation, the temperature was raised to 85-95℃ and the reaction was continued for 10-30 minutes. After the reaction was completed, the dichloroethane was removed by vacuum distillation to obtain a silicon-containing polycarboxylic acid complex stabilizer.

[0041] As a preferred embodiment of the present invention, the drying and crosslinking in step (3) adopts a staged heating method:

[0042] First stage: Keep warm at 80-100℃ for 1-3 hours;

[0043] Second stage: Keep warm at 100-130℃ for 1-4 hours;

[0044] Third stage: Keep warm at 130-160℃ for 1-5 hours.

[0045] As a preferred technical solution of the present invention, the atmosphere flow rate in the low-temperature pre-pyrolysis stage of step (4) is 0.5-5 L / min.

[0046] As a preferred embodiment of the present invention, the high-temperature calcination in step (5) adopts a two-stage calcination process:

[0047] First stage: Keep warm at 850-1000℃ for 2-4 hours;

[0048] Second stage: Keep warm at 1050~1250℃ for 2~6 hours.

[0049] Reaction Mechanism: This complexing stabilizer is generated via a mercapto-alkene radical click reaction: the carbon-carbon double bond of trimethylsilyl methacrylate undergoes efficient addition with the mercapto group of 2,3-dimercaptosuccinic acid to form a stable thioether bond, simultaneously introducing trimethylsilyl and polycarboxyl complexation sites into the molecule; the trimethylsilyl group can improve compatibility with organosilicon resin precursors, and the polycarboxyl groups can form multi-site chelates for metal ions. The reaction process has no byproducts, the structure is controllable, and it can inhibit the enrichment of metal impurities and the retention of organic residual carbon at the molecular level.

[0050] Compared with the prior art, the present invention has the following advantages:

[0051] 1. High product purity: Due to the use of organosilicon molecular-level precursors, the introduction of mineral impurities is avoided, and the purity of the obtained SiO2 can reach over 99.99%.

[0052] 2. Low carbon residue: Through a staged oxidation pyrolysis process, the organic residual carbon content can be effectively reduced, resulting in a final carbon content of less than 50 ppm.

[0053] 3. Uniform particle size: Silicon elements are uniformly distributed at the molecular scale in the resin precursor, and the particles obtained after calcination have good dispersibility.

[0054] 4. High process stability: Compared with the traditional gas phase method, the present invention has low equipment requirements, high process safety, and is suitable for large-scale production. Attached Figure Description

[0055] Figure 1 Laser particle size analysis spectrum of the product in Example 3

[0056] Figure 2 TGA spectrum of silicone resin in Example 3

[0057] Figure 3 The TGA spectrum of inorganic silica after high-temperature calcination in Example 3. Detailed Implementation

[0058] The preferred embodiments of the present invention will now be described. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0059] Example 1

[0060] (1) Precursor hydrolysis step: 100 kg of methyltrimethoxysilane was added to 180 kg of anhydrous methanol solvent, the water content of the anhydrous methanol was ≤0.2 wt%; the mixture was stirred at 20 °C to form a homogeneous system; then 18 kg of deionized water and 0.3 kg of hydrochloric acid catalyst were pre-mixed to form a hydrolysate, and slowly added dropwise to the homogeneous system within 0.5 h. The stirring speed was controlled at 350 rpm throughout the addition of the hydrolysate, and the pH of the system was controlled to be stable at 2.5. After the addition was completed, the reaction was continued at a constant temperature for 1 h to finally obtain a clear silanol hydrolysate.

[0061] (2) Polycondensation into resin step: The silanol hydrolysate obtained in step (1) is heated to 45°C for polycondensation reaction for 3 hours, so that the system gradually forms an organosilicon resin sol; the solid content of the system is controlled to be 28wt% throughout the polycondensation process; then 0.5kg complexing stabilizer is added, and the reaction is continued at a constant temperature for 0.5 hours to obtain a transparent organosilicon resin precursor liquid.

[0062] The preparation method of the complexing stabilizer is as follows: 25 kg of trimethylsilyl methacrylate, 65 kg of 2,3-dimercaptosuccinic acid, and 350 kg of anhydrous dichloroethane are added to a reaction vessel, nitrogen gas is introduced to remove oxygen for 35 minutes, 0.1 kg of azobisisobutyronitrile (AIBN) is added, the temperature is raised to 70°C and reacted for 2 hours, and under 365 nm ultraviolet light irradiation, the temperature is raised to 85°C and the reaction is continued for 10 minutes; after the reaction is completed, the dichloroethane solvent is removed by vacuum distillation to obtain a silicon-containing polycarboxyl complexing stabilizer.

[0063] (3) Resin drying and crosslinking steps: The organosilicon resin precursor liquid obtained in step (2) is subjected to de-alcoholization at 50℃ and reduced pressure of -0.04MPa for 0.5h; then the drying, crosslinking and curing are completed by three-stage heating: first stage: 80℃ for 1h; second stage: 100℃ for 1h; third stage: 130℃ for 1h; finally, a fully cured solid organosilicon resin is obtained.

[0064] (4) Low-temperature pre-pyrolysis step: The solid organosilicon resin obtained in step (3) is placed in an air atmosphere, and the flow rate of the pyrolysis atmosphere is controlled at 0.5L / min; first, the temperature is raised to 180℃ at 1℃ / min and kept for 1h to remove low-boiling organic groups and residual methoxy groups; then, the temperature is raised to 350℃ at 1℃ / min and kept for 1h to complete the complete pyrolysis and carbonization of the organic side chain.

[0065] (5) High-temperature calcination purification step: The product after pre-pyrolysis is placed in an air atmosphere and a two-stage high-temperature calcination program is adopted, with a uniform heating rate of 2℃ / min; the first stage: 850℃ for 2h; the second stage: 1050℃ for 2h; after calcination, the product is naturally cooled to room temperature in the furnace to obtain high-purity silica powder.

[0066] Example 2

[0067] (1) Precursor hydrolysis step: 120 kg of methyltrimethoxysilane and vinyltrimethoxysilane 1:1 compounded precursor was added to 220 kg of anhydrous ethanol solvent, the water content of anhydrous ethanol was ≤0.2 wt%; the mixture was stirred at 28 °C to form a homogeneous system; then 30 kg of deionized water and 1.15 kg of acetic acid catalyst were pre-mixed to form a hydrolysate, and slowly added dropwise to the homogeneous system over 1.25 h. The stirring speed was controlled at 475 rpm throughout the addition of the hydrolysate, and the pH of the system was kept stable at 3.5. After the addition was completed, the reaction was continued at a constant temperature for 2.5 h to finally obtain a clear silanol hydrolysate.

[0068] (2) Polycondensation into resin step: The silanol hydrolysate obtained in step (1) is heated to 60°C and polycondensation reaction is carried out for 6.5h, so that the system gradually forms organosilicon resin sol; the solid content of the system is controlled to be 36.5wt% throughout the polycondensation process; then 3.25kg complexing stabilizer is added and the reaction is continued at a constant temperature for 1.75h to obtain a semi-transparent organosilicon resin precursor liquid.

[0069] The preparation method of the complexing stabilizer is as follows: 30 kg of trimethylsilyl methacrylate, 70 kg of 2,3-dimercaptosuccinic acid, and 400 kg of anhydrous dichloroethane are added to a reaction vessel, nitrogen gas is introduced to remove oxygen for 42 minutes, 0.25 kg of azobisisobutyronitrile (AIBN) is added, the temperature is raised to 75°C and reacted for 3 hours, and under 365 nm ultraviolet light irradiation, the temperature is raised to 90°C and the reaction is continued for 20 minutes; after the reaction is completed, the dichloroethane solvent is removed by vacuum distillation to obtain a silicon-containing polycarboxyl complexing stabilizer.

[0070] (3) Resin drying and crosslinking steps: The organosilicon resin precursor liquid obtained in step (2) was subjected to de-alcoholization at 70℃ and reduced pressure of -0.065MPa for 1.75h; then, the drying, crosslinking and curing were completed by three-stage heating: first stage: 90℃ for 2h; second stage: 115℃ for 2.5h; third stage: 145℃ for 3h; finally, a fully cured solid organosilicon resin was obtained.

[0071] (4) Low-temperature pre-pyrolysis step: The solid organosilicon resin obtained in step (3) is placed in a nitrogen-oxygen mixed atmosphere with an oxygen content of 17.5 vol%, and the flow rate of the pyrolysis atmosphere is controlled at 2.75 L / min; first, the temperature is raised to 265℃ at 2℃ / min and held for 2.5 h to remove low-boiling-point organic groups and residual methoxy groups; then, the temperature is raised to 500℃ at 3℃ / min and held for 3 h to complete the complete pyrolysis and carbonization of the organic side chain.

[0072] (5) High-temperature calcination purification step: The product after pre-pyrolysis is placed in an oxygen / air mixed atmosphere and a two-stage high-temperature calcination program is adopted, with a uniform heating rate of 4℃ / min; the first stage: 925℃ for 3h; the second stage: 1150℃ for 4h; after calcination, the product is naturally cooled to room temperature in the furnace to obtain high-purity silica powder.

[0073] Example 3

[0074] (1) Precursor hydrolysis step: 130 kg of vinyltrimethoxysilane and phenyltrimethoxysilane 1:1 compounded precursor was added to 240 kg of anhydrous isopropanol solvent, the water content of anhydrous isopropanol was ≤0.2 wt%; the mixture was stirred at 32 °C to form a homogeneous system; then 36 kg of deionized water and 1.6 kg of nitric acid catalyst were pre-mixed to form a hydrolysate, and slowly added dropwise to the homogeneous system over 1.6 h. The stirring speed was controlled at 540 rpm throughout the addition of the hydrolysate, and the pH of the system was kept stable at 4.0. After the addition was completed, the reaction was continued at a constant temperature for 3.2 h to finally obtain a clear silanol hydrolysate.

[0075] (2) Polycondensation into resin step: The silanol hydrolysate obtained in step (1) is heated to 68°C for polycondensation reaction for 8 hours, so that the system gradually forms organosilicon resin sol; the solid content of the system is controlled to be 41wt% throughout the polycondensation process; then 4.8kg complexing stabilizer is added, and the reaction is continued at a constant temperature for 2.2 hours to obtain a semi-transparent organosilicon resin precursor liquid.

[0076] The preparation method of the complexing stabilizer is as follows: 33 kg of trimethylsilyl methacrylate, 73 kg of 2,3-dimercaptosuccinic acid, and 430 kg of anhydrous dichloroethane are added to a reaction vessel, nitrogen gas is introduced to remove oxygen for 46 minutes, 0.32 kg of azobisisobutyronitrile (AIBN) is added, the temperature is raised to 78°C and reacted for 3.5 hours, and under 365 nm ultraviolet light irradiation, the temperature is raised to 92°C and the reaction is continued for 25 minutes; after the reaction is completed, the dichloroethane solvent is removed by vacuum distillation to obtain a silicon-containing polycarboxyl complexing stabilizer.

[0077] (3) Resin drying and crosslinking steps: The silicone resin precursor liquid obtained in step (2) was subjected to de-alcoholization at 80℃ and reduced pressure of -0.08MPa for 2.4h; then, the drying, crosslinking and curing were completed by three-stage heating: first stage: 95℃ for 2.5h; second stage: 122℃ for 3.2h; third stage: 150℃ for 4h; finally, a fully cured solid silicone resin was obtained.

[0078] (4) Low-temperature pre-pyrolysis step: The solid organosilicon resin obtained in step (3) is placed in a nitrogen-oxygen mixed atmosphere with an oxygen content of 24 vol%, and the flow rate of the pyrolysis atmosphere is controlled at 4 L / min; first, the temperature is raised to 310℃ at 2.6℃ / min and held for 3.2 h to remove low-boiling organic groups and residual methoxy groups; then, the temperature is raised to 580℃ at 4℃ / min and held for 4 h to complete the complete pyrolysis and carbonization of the organic side chain.

[0079] (5) High-temperature calcination purification step: The product after pre-pyrolysis is placed in a pure oxygen atmosphere and a two-stage high-temperature calcination program is adopted, with a uniform heating rate of 5℃ / min; the first stage: 960℃ for 3.5h; the second stage: 1200℃ for 5h; after calcination, the product is naturally cooled to room temperature in the furnace to obtain high-purity silica powder.

[0080] Example 4

[0081] (1) Precursor hydrolysis step: 140 kg of methyltrimethoxysilane, vinyltrimethoxysilane and hydrogentrimethoxysilane ternary composite precursors were added to 260 kg of anhydrous n-butanol solvent, the water content of anhydrous n-butanol was ≤0.2 wt%; the mixture was stirred at 35 °C to form a homogeneous system; then 42 kg of deionized water and 2.0 kg of oxalic acid catalyst were pre-mixed to form a hydrolysate, and slowly added dropwise to the homogeneous system within 2 h. The stirring speed was controlled at 600 rpm throughout the addition of the hydrolysate, and the pH of the system was controlled to be stable at 4.5. After the addition was completed, the reaction was continued at a constant temperature for 4 h to finally obtain a clear silanol hydrolysate.

[0082] (2) Polycondensation into resin step: The silanol hydrolysate obtained in step (1) is heated to 75°C for polycondensation reaction for 10 hours, so that the system gradually forms organosilicon resin sol; the solid content of the system is controlled to be 45wt% throughout the polycondensation process; then 6kg of complexing stabilizer is added, and the reaction is continued at a constant temperature for 3 hours to obtain transparent organosilicon resin precursor liquid.

[0083] The preparation method of the complexing stabilizer is as follows: 35 kg of trimethylsilyl methacrylate, 75 kg of 2,3-dimercaptosuccinic acid, and 450 kg of anhydrous dichloroethane are added to a reaction vessel, nitrogen gas is introduced to remove oxygen for 50 minutes, 0.4 kg of azobisisobutyronitrile (AIBN) is added, the temperature is raised to 80°C and reacted for 4 hours, and then the temperature is raised to 95°C and reacted for another 30 minutes under 365 nm ultraviolet light irradiation. After the reaction is completed, the dichloroethane solvent is removed by vacuum distillation to obtain a silicon-containing polycarboxylic acid complexing stabilizer.

[0084] (3) Resin drying and crosslinking steps: The silicone resin precursor liquid obtained in step (2) was subjected to de-alcoholization at 90℃ and reduced pressure of -0.09MPa for 3h; then the drying, crosslinking and curing were completed by three-stage heating: first stage: 100℃ for 3h; second stage: 130℃ for 4h; third stage: 160℃ for 5h; finally, a fully cured solid silicone resin was obtained.

[0085] (4) Low-temperature pre-pyrolysis step: The solid organosilicon resin obtained in step (3) is placed in a nitrogen-oxygen mixed atmosphere with an oxygen content of 30 vol%, and the flow rate of the pyrolysis atmosphere is controlled at 5 L / min; first, the temperature is raised to 350℃ at 3℃ / min and kept at 4h to remove low-boiling-point organic groups and residual methoxy groups; then, the temperature is raised to 650℃ at 5℃ / min and kept at 5h to complete the complete pyrolysis and carbonization of the organic side chain.

[0086] (5) High-temperature calcination purification step: The product after pre-pyrolysis is placed in a nitrogen / oxygen mixed inert oxidizing atmosphere and a two-stage high-temperature calcination program is adopted, with a uniform heating rate of 6℃ / min; the first stage: 1000℃ for 4h; the second stage: 1250℃ for 6h; after calcination, the product is naturally cooled to room temperature in the furnace to obtain high-purity silica powder.

[0087] Comparative Example 1

[0088] (1) Precursor hydrolysis step: 100 kg of methyltrimethoxysilane was added to 180 kg of anhydrous methanol solvent, the water content of the anhydrous methanol was ≤0.2 wt%; the mixture was stirred at 20 °C to form a homogeneous system; then 18 kg of deionized water and 0.3 kg of hydrochloric acid catalyst were pre-mixed to form a hydrolysate, and slowly added dropwise to the homogeneous system within 0.5 h. The stirring speed was controlled at 350 rpm throughout the addition of the hydrolysate, and the pH of the system was controlled to be stable at 2.5. After the addition was completed, the reaction was continued at a constant temperature for 1 h to finally obtain a clear silanol hydrolysate.

[0089] (2) Polycondensation into resin step: The silanol hydrolysate obtained in step (1) is heated to 45°C for polycondensation reaction for 3 hours, so that the system gradually forms an organosilicon resin sol; the solid content of the system is controlled to be 28wt% throughout the polycondensation process; then 0.5kg of complexing stabilizer citric acid is added, and the reaction is continued at a constant temperature for 0.5 hours to obtain a transparent organosilicon resin precursor solution.

[0090] (3) Resin drying and crosslinking steps: The organosilicon resin precursor liquid obtained in step (2) is subjected to de-alcoholization at 50℃ and reduced pressure of -0.04MPa for 0.5h; then the drying, crosslinking and curing are completed by three-stage heating: first stage: 80℃ for 1h; second stage: 100℃ for 1h; third stage: 130℃ for 1h; finally, a fully cured solid organosilicon resin is obtained.

[0091] (4) Low-temperature pre-pyrolysis step: The solid organosilicon resin obtained in step (3) is placed in an air atmosphere, and the flow rate of the pyrolysis atmosphere is controlled at 0.5L / min; first, the temperature is raised to 180℃ at 1℃ / min and kept for 1h to remove low-boiling organic groups and residual methoxy groups; then, the temperature is raised to 350℃ at 1℃ / min and kept for 1h to complete the complete pyrolysis and carbonization of the organic side chain.

[0092] (5) High-temperature calcination purification step: The product after pre-pyrolysis is placed in an air atmosphere and a two-stage high-temperature calcination program is adopted, with a uniform heating rate of 2℃ / min; the first stage: 850℃ for 2h; the second stage: 1050℃ for 2h; after calcination, the product is naturally cooled to room temperature in the furnace to obtain high-purity silica powder.

[0093] Comparative Example 2

[0094] (1) Precursor hydrolysis step: 100 kg of methyltrimethoxysilane was added to 180 kg of anhydrous methanol solvent, the water content of the anhydrous methanol was ≤0.2 wt%; the mixture was stirred at 20 °C to form a homogeneous system; then 18 kg of deionized water and 0.3 kg of hydrochloric acid catalyst were pre-mixed to form a hydrolysate, and slowly added dropwise to the homogeneous system within 0.5 h. The stirring speed was controlled at 350 rpm throughout the addition of the hydrolysate, and the pH of the system was controlled to be stable at 2.5. After the addition was completed, the reaction was continued at a constant temperature for 1 h to finally obtain a clear silanol hydrolysate.

[0095] (2) Polycondensation into resin step: The silanol hydrolysate obtained in step (1) is heated to 45°C for polycondensation reaction for 3 hours, so that the system gradually forms an organosilicon resin sol; the solid content of the system is controlled to be 28wt% throughout the polycondensation process; then 0.5kg complexing stabilizer is added, and the reaction is continued at a constant temperature for 0.5 hours to obtain a transparent organosilicon resin precursor liquid.

[0096] The preparation method of the complexing stabilizer is as follows: 65 kg of 2,3-dimercaptosuccinic acid and 350 kg of anhydrous dichloroethane are added to a reaction vessel, nitrogen gas is introduced to remove oxygen for 35 minutes, 0.1 kg of azobisisobutyronitrile (AIBN) is added, the temperature is raised to 70°C and reacted for 2 hours, and then the temperature is raised to 85°C and reacted for another 10 minutes under 365 nm ultraviolet light irradiation. After the reaction is completed, the dichloroethane solvent is removed by vacuum distillation to obtain a silicon-containing polycarboxylic acid complexing stabilizer.

[0097] (3) Resin drying and crosslinking steps: The organosilicon resin precursor liquid obtained in step (2) is subjected to de-alcoholization at 50℃ and reduced pressure of -0.04MPa for 0.5h; then the drying, crosslinking and curing are completed by three-stage heating: first stage: 80℃ for 1h; second stage: 100℃ for 1h; third stage: 130℃ for 1h; finally, a fully cured solid organosilicon resin is obtained.

[0098] (4) Low-temperature pre-pyrolysis step: The solid organosilicon resin obtained in step (3) is placed in an air atmosphere, and the flow rate of the pyrolysis atmosphere is controlled at 0.5L / min; first, the temperature is raised to 180℃ at 1℃ / min and kept for 1h to remove low-boiling organic groups and residual methoxy groups; then, the temperature is raised to 350℃ at 1℃ / min and kept for 1h to complete the complete pyrolysis and carbonization of the organic side chain.

[0099] (5) High-temperature calcination purification step: The product after pre-pyrolysis is placed in an air atmosphere and a two-stage high-temperature calcination program is adopted, with a uniform heating rate of 2℃ / min; the first stage: 850℃ for 2h; the second stage: 1050℃ for 2h; after calcination, the product is naturally cooled to room temperature in the furnace to obtain high-purity silica powder.

[0100] Comparative Example 3

[0101] (1) Precursor hydrolysis step: 100 kg of methyltrimethoxysilane was added to 180 kg of anhydrous methanol solvent, the water content of the anhydrous methanol was ≤0.2 wt%; the mixture was stirred at 20 °C to form a homogeneous system; then 18 kg of deionized water and 0.3 kg of hydrochloric acid catalyst were pre-mixed to form a hydrolysate, and slowly added dropwise to the homogeneous system within 0.5 h. The stirring speed was controlled at 350 rpm throughout the addition of the hydrolysate, and the pH of the system was controlled to be stable at 2.5. After the addition was completed, the reaction was continued at a constant temperature for 1 h to finally obtain a clear silanol hydrolysate.

[0102] (2) Polycondensation into resin step: The silanol hydrolysate obtained in step (1) is heated to 45°C for polycondensation reaction for 3 hours, so that the system gradually forms an organosilicon resin sol; the solid content of the system is controlled to be 28wt% throughout the polycondensation process; then 0.5kg complexing stabilizer is added, and the reaction is continued at a constant temperature for 0.5 hours to obtain a transparent organosilicon resin precursor liquid.

[0103] The preparation method of the complexing stabilizer is as follows: 25 kg of trimethylsilyl methacrylate and 350 kg of anhydrous dichloroethane are added to a reaction vessel, nitrogen gas is introduced to remove oxygen for 35 minutes, 0.1 kg of azobisisobutyronitrile (AIBN) is added, the temperature is raised to 70°C and reacted for 2 hours, and then the temperature is raised to 85°C and reacted for another 10 minutes under 365 nm ultraviolet light irradiation. After the reaction is completed, the dichloroethane solvent is removed by vacuum distillation to obtain a silicon-containing polycarboxylic acid complexing stabilizer.

[0104] (3) Resin drying and crosslinking steps: The organosilicon resin precursor liquid obtained in step (2) is subjected to de-alcoholization at 50℃ and reduced pressure of -0.04MPa for 0.5h; then the drying, crosslinking and curing are completed by three-stage heating: first stage: 80℃ for 1h; second stage: 100℃ for 1h; third stage: 130℃ for 1h; finally, a fully cured solid organosilicon resin is obtained.

[0105] (4) Low-temperature pre-pyrolysis step: The solid organosilicon resin obtained in step (3) is placed in an air atmosphere, and the flow rate of the pyrolysis atmosphere is controlled at 0.5L / min; first, the temperature is raised to 180℃ at 1℃ / min and kept for 1h to remove low-boiling organic groups and residual methoxy groups; then, the temperature is raised to 350℃ at 1℃ / min and kept for 1h to complete the complete pyrolysis and carbonization of the organic side chain.

[0106] (5) High-temperature calcination purification step: The product after pre-pyrolysis is placed in an air atmosphere and a two-stage high-temperature calcination program is adopted, with a uniform heating rate of 2℃ / min; the first stage: 850℃ for 2h; the second stage: 1050℃ for 2h; after calcination, the product is naturally cooled to room temperature in the furnace to obtain high-purity silica powder.

[0107] Test method:

[0108] 1. SiO2 purity and metal impurity testing

[0109] The tests were performed using inductively coupled plasma mass spectrometry (ICP-MS).

[0110] Test steps:

[0111] (1) Weigh 0.1000g of the sample and place it in a polytetrafluoroethylene digestion vessel;

[0112] (2) Add 5 mL of hydrofluoric acid (HF) and 2 mL of nitric acid (HNO3);

[0113] (3) Digest at 180℃ for 40 min using a microwave digester;

[0114] (4) After digestion, bring the volume to 100 mL;

[0115] (5) The contents of metal ions such as Fe, Na, K, Ca, and Al were tested using ICP-MS;

[0116] (6) Calculate the purity of SiO2 by subtracting the total amount of impurities from 100%.

[0117] 2. Residual carbon content test

[0118] The test was conducted using an infrared carbon-sulfur analyzer.

[0119] Test steps:

[0120] (1) Weigh 0.20g of sample;

[0121] (2) Combustion in an oxygen atmosphere in a high-frequency induction furnace;

[0122] (3) Detect the infrared absorption intensity of CO2 generated by combustion;

[0123] (4) The residual carbon content is calculated.

[0124] 3. Specific surface area test (BET)

[0125] The nitrogen adsorption BET method was used for testing.

[0126] Test steps:

[0127] (1) Weigh 0.15g of sample;

[0128] (2) Degas under vacuum at 200℃ for 4 hours;

[0129] (3) N2 adsorption-desorption test was performed using a specific surface area analyzer;

[0130] (4) Calculate the specific surface area based on the BET model.

[0131] 4. Particle size distribution test

[0132] The test was conducted using a laser particle size analyzer.

[0133] Test steps:

[0134] (1) Weigh approximately 0.1 g of sample;

[0135] (2) Add ethanol and ultrasonically disperse for 15 min;

[0136] (3) Test the D5 particle size.

[0137] 5. Thermal stability test

[0138] Thermogravimetric analysis (TGA) was used for testing.

[0139] Test conditions:

[0140] Oxygen atmosphere;

[0141] Heating rate: 10℃ / min;

[0142] Test range: 30–1000℃.

[0143] Record the total weight loss rate of the sample.

[0144] Table 1 Results of Chemical Purity and Residual Carbon Tests

[0145] <![CDATA[Purity of SiO2 / %]]> Fe / ppm Na / ppm Ca / ppm Residual carbon / ppm Example 1 99.991 7 11 6 39 Example 2 99.992 5 9 4 33 Example 3 99.994 4 8 4 25 Example 4 99.996 4 6 3 19 Comparative Example 1 99.980 13 18 11 58 Comparative Example 2 99.987 10 14 8 45 Comparative Example 3 99.989 9 13 8 41

[0146] Table 2. Test results of particle size, specific surface area, and thermal stability.

[0147] D50 / μm <![CDATA[BET specific surface area / m 2 / g]]> Total weight loss at 1000℃ / % Example 1 0.81 177 0.51 Example 2 0.73 190 0.47 Example 3 0.95 202 0.42 Example 4 0.77 214 0.40 Comparative Example 1 0.88 153 0.76 Comparative Example 2 0.80 166 0.61 Comparative Example 3 0.850 170 0.58

[0148] A silicon-containing polycarboxylic acid complex stabilizer prepared by the mercapto-click reaction of trimethylsilyl methacrylate and 2,3-dimercaptosuccinic acid can significantly improve the overall performance of high-purity silica.

[0149] This stabilizer achieves precise bonding between silicon-based and polycarboxyl groups through mercapto-olefin click, and the trimethylsilyl group enhances the interfacial compatibility and dispersibility with the silicon-based precursor, resulting in a narrower particle size distribution and a higher specific surface area of ​​the product.

[0150] The multiple carboxyl sites provided by 2,3-dimercaptosuccinic acid enable strong chelation of metal ions, significantly reducing the levels of impurities such as Fe, Na, and Ca, and improving the chemical purity of silica.

[0151] The stable structure formed by the click reaction, combined with the gradient calcination process, enables more complete removal of organic components, lower residual carbon, and better thermal stability, resulting in overall performance that is significantly superior to conventional complexing agent systems.

[0152] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity silica based on a trimethoxysilane precursor, characterized in that, Includes the following steps: (1) Precursor hydrolysis steps According to the mass fraction, 100-140 parts of trimethoxysilane were added to 180-260 parts of anhydrous alcohol solvent, and stirred at 20-35°C to form a homogeneous system; then 18-42 parts of deionized water and 0.3-2.0 parts of acidic catalyst were pre-mixed to form a hydrolysate, which was slowly added dropwise to the homogeneous system over 0.5-2 hours, controlling the pH of the system to be 2.5-4.5, and the reaction was continued for 1-4 hours to obtain a silanol hydrolysate; (2) Polycondensation into resin step The silanol hydrolysate obtained in step (1) was heated to 45–75°C for a polycondensation reaction for 3–10 h to gradually form an organosilicon resin sol. Then, 0.5–6 parts of a complexing stabilizer were added, and the reaction continued for 0.5–3 h to obtain a transparent or semi-transparent organosilicon resin precursor solution. The solid content of the system was controlled to be 28–45 wt% during the polycondensation process. (3) Resin drying and crosslinking steps The organosilicon resin precursor liquid obtained in step (2) is subjected to de-alcoholization under reduced pressure at 50-90℃ for 0.5-3h, and then dried at 80-160℃ to allow the organosilicon resin to undergo further cross-linking and curing, thereby obtaining solid organosilicon resin; the reduced pressure is controlled to be -0.04 to -0.09MPa. (4) Low-temperature pre-pyrolysis step The solid organosilicon resin obtained in step (3) is placed in an air atmosphere or a mixed atmosphere with an oxygen content of 5-30 vol%, and heated to 180-350°C at 1-3°C / min and held for 1-4 hours to remove low-boiling organic groups and residual methoxy groups; then the temperature is further increased to 350-650°C at 1-5°C / min and held for 1-5 hours to cause the organic side chains to crack and carbonize. (5) High-temperature calcination purification step The pre-pyrolysis product is placed in an air atmosphere, an oxygen atmosphere, or an inert / oxygen mixed atmosphere, heated to 850-1250℃ at a rate of 2-6℃ / min and held at that temperature. After cooling, high-purity silica powder is obtained. In step (2), the complexing stabilizer is prepared by reacting trimethylsilyl methacrylate, 2,3-dimercaptosuccinic acid, and azobisisobutyronitrile under ultraviolet light.

2. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: The trimethoxysilane is one or a combination of two or more of methyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, and hydrotrimethoxysilane.

3. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: The alcohol solvent is one or more of methanol, ethanol, isopropanol, and n-butanol, and the water content in the alcohol solvent is ≤0.2wt%.

4. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: The acidic catalyst is one or more of hydrochloric acid, nitric acid, formic acid, acetic acid, or oxalic acid.

5. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: In step (1), the stirring speed is controlled at 350-600 rpm when adding the hydrolysate.

6. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: The preparation method of the complexing stabilizer in step (2) is as follows: According to the mass fractions, 25-35 parts of trimethylsilyl methacrylate, 65-75 parts of 2,3-dimercaptosuccinic acid, and 350-450 parts of anhydrous dichloroethane were added to a reaction vessel. Nitrogen gas was introduced to remove oxygen for 35-50 minutes. Then, 0.1-0.4 parts of azobisisobutyronitrile (AIBN) were added, and the temperature was raised to 70-80°C for 2-4 hours. Under 365nm ultraviolet light irradiation, the temperature was raised to 85-95°C and the reaction was continued for 10-30 minutes. After the reaction was completed, dichloroethane was removed by vacuum distillation to obtain a silicon-containing polycarboxylic acid complex stabilizer.

7. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: In step (3), the drying and crosslinking process adopts a staged heating method: First stage: Keep warm at 80-100℃ for 1-3 hours; Second stage: Keep warm at 100-130℃ for 1-4 hours; Third stage: Keep warm at 130-160℃ for 1-5 hours.

8. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: In step (4), the atmosphere flow rate during the low-temperature pre-pyrolysis stage is 0.5–5 L / min.

9. The method for preparing high-purity silica based on a trimethoxysilane precursor according to claim 1, characterized in that: The high-temperature calcination in step (5) adopts a two-stage calcination process: First stage: Keep warm at 850-1000℃ for 2-4 hours; Second stage: Keep warm at 1050~1250℃ for 2~6 hours.

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