High true density solid silica microspheres and method for making same

Abstract

The application discloses high-true-density solid silicon dioxide microspheres and a preparation method thereof, relates to the technical field of nano inorganic functional material preparation, and the preparation method comprises the following steps: (1) mixing anhydrous ethanol, deionized water and ammonia water to obtain an alkaline catalytic premix; (2) mixing and diluting tetraethyl orthosilicate with anhydrous ethanol to obtain a homogeneous silicon source diluent, and the homogeneous silicon source diluent is injected into the alkaline catalytic premix in a two-stage differential rate dropping mode to react; (3) after the reaction is completed, a stepwise temperature rising aging process is adopted to gradually strengthen the cross-linking of silicon-oxygen bonds; (4) an alcohol washing-water washing-weak acid washing composite impurity removal process is adopted to remove organic residues, water-soluble impurities and metal ion impurities in stages; and (5) after the filter cake after washing is dried, a segmented low-temperature sintering treatment is conducted, and the high-true-density solid silicon dioxide microspheres are obtained after cooling. The application solves the problems of existing silicon dioxide microspheres, such as many internal pores and low true density.

Description

Technical Field

[0001] This invention relates to the field of nano-inorganic functional materials preparation technology, specifically to a high true density solid silica microsphere and its preparation method. Background Technology

[0002] The sol-gel method (Stöber process) is currently the mainstream process for preparing monodisperse spherical silica. It mainly utilizes the hydrolysis-condensation reaction of tetraethyl orthosilicate (TEOS) in an alkaline catalytic system to prepare silica microspheres with controllable particle size and good sphericity. Due to its simple process, adjustable particle size, and excellent mass production capabilities, it is widely used in many fields such as displays, semiconductors, optics, chemicals, and biomedicine. However, silica microspheres prepared by the traditional Stöber process have inherent structural defects, which greatly limit their application in high-end precision fields. 1. The true density is relatively low, generally only 1.9~2.05 g / cm³. 3 It is far lower than the theoretical true density of amorphous silica, which is 2.20~2.25 g / cm³. 3 The microspheres contain a large number of micropores and mesopores, exhibiting a porous / semi-hollow structure. Their overall mechanical strength and structural stability are poor, which cannot meet the requirements of high-end applications such as precision filling, wear resistance, and pressure resistance. 2. The specific surface area is relatively high. The BET microspheres with a particle size of 300nm~10μm generally have a large specific surface area. A large number of unsaturated silanol groups remain on the surface of the microspheres, which are prone to agglomeration and flocculation in the polymer resin system, causing the viscosity of the system to rise abnormally and the dispersion uniformity to be poor, which affects the processing accuracy and molding quality of the end product. 3. The porous structure readily adsorbs residual raw materials, metal ions, and halogen impurities from the aquatic environment, leading to the formation of Na+ in the microspheres. + Cl - High levels of impurities and excessive conductivity can easily lead to problems such as corrosion, leakage, aging failure, and image retention in electronic devices, making it difficult to meet the ultra-high purity and low ion contamination requirements of the electronics, semiconductor, and display industries.

[0003] Currently, the industry primarily addresses the issues of poor density and low purity of traditional silica microspheres by employing single-process optimization methods, mainly including extending aging time, increasing sintering temperature, and simply optimizing raw material ratios. However, existing improvement technologies suffer from significant technical bottlenecks and cannot achieve synergistic optimization of multiple properties. 1. Simply extending the aging time at room temperature / low temperature can only repair a few defects on the surface of the microspheres and improve the surface condensation degree, but it cannot eliminate the original pores inside the particles. The increase in true density is extremely small, reaching a maximum of only 2.15 g / cm³. 3 It is impossible to achieve a dense solid structure; 2. Although sintering at temperatures above 900℃ can close some pores and increase true density, it is very easy to cause microspheres to melt and stick together, abnormally grow in size, and become distorted in sphericity. The particle size distribution CV value increases significantly, and the monodisperse characteristics are completely lost. The product precision cannot meet the requirements of high-end precision applications. 3. It cannot simultaneously achieve core indicators such as high true density, high monodispersity, low specific surface area, low ionic impurities, and high sphericity, and has obvious limitations in technical adaptability, making it unable to meet the application needs of high-end precision materials in multiple fields. Summary of the Invention

[0004] Addressing the issues of numerous internal pores and low true density in silica microspheres prepared by the sol-gel method in existing technologies, this invention aims to provide a high-true-density solid silica microsphere and its preparation method. Through a synergistic coupling process of segmented hydrolysis, gradient temperature condensation, multi-stage impurity removal, and segmented low-temperature sintering, the internal density of the microspheres is significantly improved, while surface hydroxyl groups and specific surface area are reduced, and ionic impurity residues are strictly controlled, while ensuring excellent sphericity and monodispersity of the microspheres. This achieves a multi-dimensional performance synergistic optimal solution and can be widely adapted to high-end precision applications in fields such as display, semiconductor, optics, and biomedicine.

[0005] This invention is achieved through the following technical solution: In a first aspect, this application provides a method for preparing high-density solid silica microspheres, comprising the following steps: (1) Mix anhydrous ethanol, deionized water and ammonia water to obtain an alkaline catalytic premix; (2) Tetraethyl orthosilicate is mixed and diluted with anhydrous ethanol to obtain a homogeneous silicon source dilution. The homogeneous silicon source dilution is injected into the alkaline catalytic premix for reaction using a two-stage differential rate dropwise addition method. (3) After the reaction is completed, a step-by-step heating and aging process is adopted to gradually strengthen the cross-linking of silicon-oxygen bonds; (4) A composite impurity removal process of alcohol washing-water washing-weak acid washing is adopted to remove organic residues, water-soluble impurities and metal ion impurities in stages; (5) After the washed filter cake is dried, it is subjected to segmented low-temperature sintering treatment and cooled to obtain high-density solid silica microspheres.

[0006] This invention achieves complete separation of nucleation and growth by adding silicon source in stages at high and low speeds. Combined with a multi-gradient heating condensation mechanism, it allows microspheres to complete silicon-oxygen bond crosslinking layer by layer from the surface to the inside, eliminating internal pore defects from the source of the reaction. This overcomes the inherent shortcomings of the traditional Stöber method porous structure and significantly improves the overall density and structural stability of the microspheres.

[0007] This invention overcomes the drawbacks of traditional high-temperature sintering which is prone to adhesion and low-temperature sintering which results in poor density. It adopts gradient heating and precise sintering in a low-temperature range, achieving pore closure and complete hydroxyl condensation in the optimal temperature range of 600℃ to 850℃. While fully preserving the sphericity and monodispersity of the microspheres, the true density is increased to the theoretical limit range of amorphous silica.

[0008] The process parameters of this invention have a wide adjustable range and strong adaptability. They do not require high-end precision equipment and are compatible with laboratory small-scale, pilot-scale and industrial mass production. They can be customized to prepare a full range of particle size products from 300 nm to 1.0 μm, and are suitable for high-end applications in multiple fields.

[0009] Further, in step (1), the volume ratio of anhydrous ethanol, deionized water and ammonia is (10~30):5:(1~4), and the mass concentration of ammonia is 25wt%~28wt%.

[0010] Further, in step (2), the volume ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:(0.8~1.2).

[0011] Further, in step (2), the two-stage differentiated rate dripping method is as follows: First stage: Add 55% to 75% of the total silicon source mass at a rate of 0.4 mL / min to 1.2 mL / min. After the addition is completed, stir at a constant temperature to complete uniform nucleation and initial particle growth. The stirring time can be 1 h to 2.5 h.

[0012] The second stage involves adding the remaining 25%–45% silicon source dilution solution dropwise at a rate of 0.2 mL / min to 0.6 mL / min, followed by constant temperature stirring after the addition is complete, to achieve slow and uniform particle growth. This step can suppress the formation of internal micropores and defects from the source. The stirring time can be 2 to 3.5 hours.

[0013] Further, in step (3), the stepped heating aging process is as follows: First stage: Keep warm and stir at 40℃~55℃ for 2h~4h to promote the initial cross-linking and condensation of silanol groups on the surface of microspheres; Second stage: Keep warm and stir at 60℃~75℃ for 3h~6h to enhance the condensation reaction of silanol groups inside the particles, fill the internal pores, and build a dense silicon-oxygen network. The third stage: allow the temperature to drop naturally to room temperature and let it stand for 12 to 30 hours to achieve stable and dense particle structure.

[0014] Further, in step (4), the alcohol washing-water washing-weak acid washing composite impurity removal process is as follows: Use anhydrous ethanol for centrifugal washing to remove unreacted silicon sources and organic alcohol residues; the number of times anhydrous ethanol is used for washing can be 3 to 6.

[0015] Use deionized water for centrifugal washing to remove water-soluble impurities such as ammonia and ammonium salts; the number of times deionized water is used for washing can be 3 to 6.

[0016] Washing with dilute hydrochloric acid helps to complex and remove metal cation impurities; the washing with dilute hydrochloric acid can be performed 1 to 2 times.

[0017] Wash repeatedly with deionized water until the filtrate is neutral and the conductivity meets the standard.

[0018] Furthermore, the concentration of the dilute hydrochloric acid is 0.01 mol / L to 0.08 mol / L.

[0019] Furthermore, the drying temperature in step (5) is controlled at 60℃~120℃. The drying time can be 6h~18h.

[0020] Further, in step (5), the method for segmented low-temperature sintering is as follows: First, raise the temperature to 350℃~450℃ at a rate of 1℃ / min~3℃ / min, and hold for 1h~2.5h to remove adsorbed water, free hydroxyl groups and trace organic residues from the particle surface; Then, the temperature is increased to 600℃~850℃ at a low speed of 0.5℃ / min~2℃ / min and held for 1.5h~4h to promote the deep condensation of residual hydroxyl groups inside the particles, close the internal micropore defects, and achieve overall structural densification.

[0021] Secondly, this application provides a high-density solid silica microsphere, which is prepared by the above-mentioned preparation method.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) Extremely high density and excellent structural stability: The true density of the silica microspheres prepared in this invention is stably controlled at 2.20 g / cm³. 3 ~2.25g / cm 3 Compared with traditional processes, it improves by 5% to 18%, has no obvious micropores or mesopores, and has a complete solid and dense structure. Its mechanical compressive strength and wear resistance are greatly improved, which can meet the mechanical requirements of precision filling, wear-resistant coating, structural reinforcement and other scenarios. (2) Extremely low specific surface area and hydroxyl residue: The BET specific surface area of ​​microspheres with a particle size of 300nm~1.0μm can be stably controlled at 2.5m. 2 / g~5.0m 2 / g, with a significantly reduced surface hydroxyl value, exhibits excellent dispersibility in various polymer resin systems such as epoxy, PI, and acrylic, effectively suppressing the increase in adhesive viscosity, and is suitable for high-precision coating, precision injection molding, film modification and other processes. (3) Ultra-high purity and ultra-low ion contamination: Through a multi-stage composite impurity removal process, the product Na + ≤5mg / Kg, Cl - ≤20mg / Kg, system conductivity ≤10μS / cm, no heavy metal residue, can completely avoid the problems of ion corrosion, leakage and aging failure of electronic devices, and is suitable for high reliability scenarios such as semiconductor packaging, electronic insulation materials, and high-end display devices. (4) Excellent monodispersity and sphericity: The particle size distribution CV value of the microspheres is stable at ≤5%, with the best reaching 2.5%~4%, and the sphericity is ≥98%. There are no irregular particles or agglomerated large particles, and the particle size uniformity is excellent, which meets the high precision requirements of optical precision fillers, precision spacers and high-end polishing materials. (5) Strong process versatility and high mass production stability: The core process parameters have a wide adjustable range and good repeatability. The batch-to-batch performance fluctuation error is ≤3%. The particle size, density and purity indicators are stable and controllable, and can be mass-produced on a large scale. The product particle size can be customized arbitrarily within the range of 300nm~1.0μm, and it is widely applicable to high-end applications in many fields such as display panel functional materials, semiconductor packaging fillers, precision optical coatings, high-end wear-resistant coatings, biomedical carriers, electronic insulating fillers, and precision polishing materials. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a SEM image of the high true density solid silica microspheres prepared in Example 1 of this invention; Figure 2 This is a SEM image of the high true density solid silica microspheres prepared in Example 2 of the present invention; Figure 3 SEM image of the silica microspheres prepared in Comparative Example 1; Figure 4 SEM image of the silica microspheres prepared in Comparative Example 2; Figure 5 SEM image of the silica microspheres prepared in Comparative Example 3; Figure 6 The Fourier transform infrared spectra of the silica microspheres prepared in Examples 1, 2, and 1 are shown.

[0024] Figure 7 Fourier transform infrared spectra of the silica microspheres prepared in Comparative Examples 2 and 3. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0026] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0027] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described herein, as well as the features of those different embodiments or examples.

[0028] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0030] Example 1

[0031] This embodiment provides a method for preparing 500 nm high-density solid silica microspheres, the specific steps of which are as follows: S1. Preparation of alkaline catalytic premix: Mix 270 mL of anhydrous ethanol, 100 mL of deionized water, and 30 mL of 25 wt% ammonia water, stir evenly, and heat to 30 °C to obtain alkaline catalytic premix.

[0032] S2. Segmented gradient hydrolysis nucleation and growth: Mix 30 mL of tetraethyl orthosilicate (TEOS) with 30 mL of anhydrous ethanol to obtain a homogeneous silicon source dilution; inject the homogeneous silicon source dilution into the alkaline catalytic premix solution using a two-stage differential rate addition method for reaction: In the first stage, 70% diluent (40 mL) was added dropwise at 0.8 mL / min, and the mixture was kept warm and stirred for 1.5 h to complete uniform nucleation and initial particle growth. In the second stage, the remaining 30% diluent (20 mL) was added dropwise at 0.3 mL / min, and the mixture was kept warm and stirred for 2.5 h to achieve slow and uniform particle growth and suppress the formation of internal micropores and defects from the source.

[0033] S3, Multi-stage gradient heating aging condensation: After the reaction, a step-by-step heating aging process is used to progressively strengthen the cross-linking of silicon-oxygen bonds. First stage: Keep warm at 45℃ and stir for 3 hours to promote the initial cross-linking and condensation of silanol groups on the surface of microspheres; Second stage: Keep warm at 60℃ and stir for 5 hours to enhance the condensation reaction of silanol groups inside the particles, fill the internal pores, and build a dense silicon-oxygen network. The third stage: allow the temperature to drop naturally to room temperature and let it stand for 18 hours to achieve stable and dense particle structure.

[0034] S4. Multi-stage alternating washing and impurity removal: A composite impurity removal process of alcohol washing, water washing, and weak acid washing is adopted to remove organic residues, water-soluble impurities, and metal ion impurities in stages. The sample was washed four times by centrifugation with anhydrous ethanol to remove unreacted silicon sources and organic alcohol residues. The sample was washed four times by centrifugation with deionized water to remove water-soluble impurities such as ammonia and ammonium salts. The solution was washed once with 0.02 mol / L dilute hydrochloric acid to complex and remove metal cation impurities. Finally, it was repeatedly washed with deionized water until the filtrate was neutral and the conductivity met the standard.

[0035] S5. Segmented low-temperature sintering densification: The washed filter cake is dried at 100℃ for 12 hours, and then placed in a muffle furnace for segmented low-temperature sintering treatment. The temperature was increased to 400℃ at a rate of 2℃ / min and held for 2 hours to remove adsorbed water, free hydroxyl groups and trace organic residues from the particle surface. The temperature was increased to 700℃ at a low rate of 2℃ / min and held for 4 hours to promote the deep condensation of residual hydroxyl groups inside the particles, close the internal micropore defects, and achieve overall structural densification. After natural cooling to room temperature, high-density, high-purity, monodisperse silica microspheres were obtained by sieving.

[0036] The relevant properties of the prepared silica microspheres were tested, such as... Figure 1 The image shows a SEM image of silica microspheres. As can be seen from the image, the particles are monodisperse spherical with smooth surfaces and a CV value of 3.26%, indicating good particle size uniformity.

[0037] from Figure 6 The above shows 1115, 810, and 476 cm. -1The peaks are typical infrared characteristic peaks of amorphous silica, and there are no characteristic peaks of hydroxyl groups or other substances, indicating that the silica sample is thoroughly dried and has high purity, with no other organic residues.

[0038] Example 2

[0039] This embodiment provides a method for preparing 700 nm high-density solid silica microspheres, the specific steps of which are as follows: S1. Preparation of alkaline catalytic premix: Mix 270 mL of anhydrous ethanol, 100 mL of deionized water, and 50 mL of 28 wt% ammonia water, stir evenly, and heat to 30 °C to obtain alkaline catalytic premix.

[0040] S2. Segmented gradient hydrolysis nucleation and growth: Mix 50 mL of tetraethyl orthosilicate (TEOS) with 50 mL of anhydrous ethanol to obtain a homogeneous silicon source dilution; inject the homogeneous silicon source dilution into the alkaline catalytic premix solution using a two-stage differential rate addition method for reaction: In the first stage, 65% diluent (65 mL) is added dropwise at 1.0 mL / min, and the mixture is kept warm and stirred for 2 hours to complete uniform nucleation and initial particle growth. In the second stage, the remaining 35% diluent (35 mL) is added dropwise at 0.4 mL / min, and the mixture is kept warm and stirred for 3 hours to achieve slow and uniform particle growth, thereby inhibiting the formation of internal micropores and defects from the source.

[0041] S3, Multi-stage gradient heating aging condensation: After the reaction, a step-by-step heating aging process is used to progressively strengthen the cross-linking of silicon-oxygen bonds. First stage: Keep warm at 40℃ and stir for 4 hours to promote the initial cross-linking and condensation of silanol groups on the surface of microspheres; Second stage: Keep warm at 65℃ and stir for 4 hours to enhance the condensation reaction of silanol groups inside the particles, fill the internal pores, and build a dense silicon-oxygen network. The third stage: allow the temperature to drop naturally to room temperature and let it stand for 24 hours to achieve stable and dense particle structure.

[0042] S4. Multi-stage alternating washing and impurity removal: A composite impurity removal process of alcohol washing, water washing, and weak acid washing is adopted to remove organic residues, water-soluble impurities, and metal ion impurities in stages. The sample was washed four times by centrifugation with anhydrous ethanol to remove unreacted silicon sources and organic alcohol residues. The sample was washed four times by centrifugation with deionized water to remove water-soluble impurities such as ammonia and ammonium salts. The solution was washed once with 0.02 mol / L dilute hydrochloric acid to complex and remove metal cation impurities. Finally, it was repeatedly washed with deionized water until the filtrate was neutral and the conductivity met the standard.

[0043] S5. Segmented low-temperature sintering densification: The washed filter cake is dried at 100℃ for 12 hours, and then placed in a muffle furnace for segmented low-temperature sintering treatment. The temperature was increased to 400℃ at a rate of 2℃ / min and held for 2 hours to remove adsorbed water, free hydroxyl groups and trace organic residues from the particle surface. The temperature was increased to 800℃ at a low rate of 2℃ / min and held for 2h to promote the deep condensation of residual hydroxyl groups inside the particles, close the internal micropore defects, and achieve overall structural densification. After natural cooling to room temperature, high-density, high-purity, monodisperse silica microspheres were obtained by sieving.

[0044] The relevant properties of the prepared silica microspheres were tested, such as... Figure 2 The image shows a SEM image of silica microspheres. As can be seen from the image, the particles are monodisperse spherical with smooth surfaces and good particle size uniformity, and the CV value is 2.89%.

[0045] from Figure 6 As can be seen above, in the infrared spectrum, 1115 cm⁻¹ -1 812cm -1 and 476 cm -1 The sample exhibits typical characteristic peaks of amorphous silica, with accurate and sharp peak positions. No significant absorption is observed in the hydroxyl vibration region or the organic functional group region, indicating that the sample is free of bound water, silanol groups, and organic residues. Furthermore, the hydroxyl value is lower than that of Example 1, quantitatively confirming its greater dryness. In summary, this silica exhibits high purity, low moisture content, and no organic contamination, meeting the application requirements in the field of electronic materials.

[0046] Comparative Example 1 This comparative example uses the traditional Stöber method to prepare 500 nm microspheres. The traditional one-step Stöber method is used (the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in an alcohol solvent catalyzed by ammonia water to obtain silica nanospheres with controllable particle size and high monodispersity). The remaining parameters are the same as in Example 1, and gradient aging and low-temperature sintering are not performed.

[0047] The relevant properties of the prepared silica microspheres were tested, such as... Figure 3 The image shows an SEM image of the silica microspheres. As can be seen from the image, the microspheres are still monodisperse spherical particles with smooth surfaces, but the particle size distribution is wider and the CV value is 6.02%.

[0048] from Figure 6 As can be seen above, in the infrared spectrum, except for 1103 cm⁻¹ -1 800cm -1 468 cm -1 In addition to the characteristic peaks of amorphous silica, several impurity peaks also appear: ~3414 cm⁻¹ -1 Broad peak (-OH stretching), ~1636 cm⁻¹ -1 (HOH bend) and ~954 cm-1 (≡Si-OH stretching). These absorptions indicate that the microspheres contain a large amount of adsorbed and bound water, are highly hydrophilic, and easily absorb moisture. Therefore, the moisture content of this sample is significantly higher than expected.

[0049] Comparative Example 2 The comparative example involves sintering the sample prepared in Comparative Example 1 at a high temperature of 400℃.

[0050] like Figure 4 The image shows a SEM image of the silica microspheres. As can be seen from the image, the microspheres are monodisperse spherical particles with smooth surfaces and a CV value of 6.15%.

[0051] from Figure 7 As can be seen above, in the infrared spectrum, 1108, 810, and 471 cm⁻¹ -1 The peaks are characteristic of amorphous silicon dioxide, while ~3435 cm⁻¹ is... -1 Broad peak (-OH stretching), ~1636 cm⁻¹ -1 (HOH bending). Some adsorbed water and bound water still remain on the surface of the sample.

[0052] Comparative Example 3 The comparative example involves sintering the sample prepared in Comparative Example 1 at a high temperature of 1000℃.

[0053] like Figure 5 The image shows a SEM image of the silica microspheres. It can be seen that high temperature caused significant sintering, adhesion, and agglomeration between the microspheres, resulting in a loose arrangement of microspheres and a large number of tiny debris particles in the sample background. This is due to the condensation and dehydration of surface silanol groups at high temperature, leading to bridging between microspheres, or the decomposition of a small amount of unreacted precursors at high temperature.

[0054] from Figure 7 As can be seen above, after calcination at 1000℃, the hydroxyl groups (3435 cm⁻¹) in the infrared spectrum... -1 ) and physically adsorbed water (1636 cm) -1 The absorption peak of ) has completely disappeared, indicating that the bound water and hydroxyl groups on the surface of the microspheres have been completely removed; at the same time, the absorption peak of 1031 cm⁻¹ ... -1 808 cm -1 and 438 cm -1 The presence of Si-O-Si vibrational peaks in the region indicates that the silica framework of the sample still maintains an amorphous structure.

[0055] The relevant properties of the silica microspheres prepared by the methods of Examples 1-2 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0056] Table 1

[0057] The test results above show that Examples 1 and 2 exhibit significant advantages in particle morphology compared to the comparative examples: intact sphericity, no surface breakage, lower CV values, narrower particle size distribution, and significantly improved particle uniformity. In terms of physical properties, both maintain practical true density and moderate specific surface area, balancing reactivity and processing stability. Regarding chemical purity, both have low hydroxyl values ​​and low moisture content, with few ionic impurities, which helps reduce interference with the performance of electronic materials. Considering these characteristics, Examples 1 and 2 are more suitable for the field of electronic materials where stringent requirements for purity and consistency are necessary.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing high-density solid silica microspheres, characterized in that, Includes the following steps: (1) Mix anhydrous ethanol, deionized water and ammonia water to obtain an alkaline catalytic premix; (2) Tetraethyl orthosilicate is mixed and diluted with anhydrous ethanol to obtain a homogeneous silicon source dilution. The homogeneous silicon source dilution is injected into the alkaline catalytic premix for reaction using a two-stage differential rate dropwise addition method. (3) After the reaction is completed, a step-by-step heating and aging process is adopted to gradually strengthen the cross-linking of silicon-oxygen bonds; (4) A composite impurity removal process of alcohol washing-water washing-weak acid washing is adopted to remove organic residues, water-soluble impurities and metal ion impurities in stages; (5) After the washed filter cake is dried, it is subjected to segmented low-temperature sintering treatment and cooled to obtain high-density solid silica microspheres.

2. The method for preparing high-density solid silica microspheres according to claim 1, characterized in that, In step (1), the volume ratio of anhydrous ethanol, deionized water and ammonia is (10~30):5:(1~4), and the mass concentration of ammonia is 25wt%~28wt%.

3. The method for preparing high-density solid silica microspheres according to claim 1, characterized in that, In step (2), the volume ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:(0.8~1.2).

4. The method for preparing high-density solid silica microspheres according to claim 1, characterized in that, In step (2), the two-stage differentiated rate dripping method is as follows: First stage: Add 55% to 75% of the total silicon source mass at a rate of 0.4 mL / min to 1.2 mL / min. After the addition is completed, stir at a constant temperature to complete uniform nucleation and initial particle growth. Second stage: Add the remaining 25% to 45% silicon source dilution solution dropwise at a low speed of 0.2 mL / min to 0.6 mL / min. After the addition is completed, stir at a constant temperature to achieve slow and uniform particle growth.

5. The method for preparing high-density solid silica microspheres according to claim 1, characterized in that, In step (3), the stepped heating aging process is as follows: First stage: Keep warm and stir at 40℃~55℃ for 2h~4h to promote the initial cross-linking and condensation of silanol groups on the surface of microspheres; Second stage: Keep warm and stir at 60℃~75℃ for 3h~6h to enhance the condensation reaction of silanol groups inside the particles, fill the internal pores, and build a dense silicon-oxygen network. The third stage: allow the temperature to drop naturally to room temperature and let it stand for 12 to 30 hours to achieve stable and dense particle structure.

6. The method for preparing high-density solid silica microspheres according to claim 1, characterized in that, In step (4), the alcohol washing-water washing-weak acid washing composite impurity removal process is as follows: Use anhydrous ethanol to centrifuge and wash to remove unreacted silicon sources and organic alcohol residues; Use deionized water for centrifugal washing to remove water-soluble impurities such as ammonia and ammonium salts; Wash with dilute hydrochloric acid to complex and remove metal cation impurities; Wash repeatedly with deionized water until the filtrate is neutral and the conductivity meets the standard.

7. The method for preparing high-density solid silica microspheres according to claim 6, characterized in that, The concentration of the dilute hydrochloric acid is 0.01 mol / L to 0.08 mol / L.

8. The method for preparing high-density solid silica microspheres according to claim 1, characterized in that, The drying temperature in step (5) is controlled at 60℃~120℃.

9. The method for preparing high-density solid silica microspheres according to claim 1, characterized in that, In step (5), the method for segmented low-temperature sintering is as follows: First, raise the temperature to 350℃~450℃ at a rate of 1℃ / min~3℃ / min, and hold for 1h~2.5h to remove adsorbed water, free hydroxyl groups and trace organic residues from the particle surface; Then, the temperature is increased to 600℃~850℃ at a low speed of 0.5℃ / min~2℃ / min and held for 1.5h~4h to promote the deep condensation of residual hydroxyl groups inside the particles, close the internal micropore defects, and achieve overall structural densification.

10. A high-density solid silica microsphere, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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