Silicon dioxide and preparation method and application thereof

Abstract

The invention discloses silicon dioxide as well as a preparation method and application thereof. The preparation method comprises the following steps: adding an inorganic dispersant containing sulfate and phosphate into water glass, mixing with an organic dispersant, carrying out heat treatment to form a first mixed solution, adding the first mixed solution into a sulfuric acid solution in batches, carrying out a reaction, stopping the mixing process when the pH value of a reaction system is 2.5-3.5, and aging the reaction system to form a second mixed solution; and carrying out solid-liquid separation on the second mixed solution, washing, and then carrying out at least two-stage refining to prepare silicon dioxide. The performance of the water glass solution is improved by adopting the specific dispersing agent, so that ellipsoidal silicon dioxide with small and uniform particle size is generated in the reaction process, the surface appearance and the particle morphology of particles are further regulated and controlled through a two-stage refining process, and the ellipsoidal silicon dioxide can be used for precise polishing of high-hardness materials; the polishing efficiency and the polishing effect are greatly improved, and production and application of high-performance devices are promoted.

Description

Technical Field

[0001] This invention relates to the field of silicon dioxide technology, and in particular to silicon dioxide, its preparation method, and its applications. Background Technology

[0002] Silica is a widely used inorganic material in industry, possessing excellent properties such as high hardness, wear resistance, corrosion resistance, and thermal stability. It is widely used as an abrasive in polishing, for example, in the manufacture of metals, ceramics, glass, optical devices, and semiconductor materials. However, polishing some high-hardness materials requires high-performance polishing materials. For instance, sapphire, widely used in LED substrates, optical windows, consumer electronics covers (such as smartphone camera covers and watch screens), and military protective equipment, has extremely high hardness and surface finish requirements, making precision polishing a current technical challenge. Existing silica polishing materials are ineffective at polishing such materials, exhibiting low efficiency and failing to meet industrial application standards, thus limiting their industrial applications. Summary of the Invention

[0003] Therefore, it is necessary to provide a type of silica with high polishing efficiency and good polishing effect to achieve surface polishing of materials with high hardness and high surface precision requirements.

[0004] In a first aspect, the present invention provides a method for preparing silicon dioxide, comprising the following steps:

[0005] An inorganic dispersant and an organic dispersant are added to water glass, mixed, heat-treated, and stirred to form a first mixture; the inorganic dispersant includes sulfates and phosphates.

[0006] While stirring, the first mixture is added to the sulfuric acid solution in batches to carry out the reaction. When the pH of the reaction system is 2.5-3.5, the addition of the first mixture to the sulfuric acid solution is stopped, and the reaction system is aged to form the second mixture.

[0007] The second mixture is subjected to solid-liquid separation and washing to form a slurry. The slurry is then refined at least in two stages to prepare silica.

[0008] In some embodiments, the concentration of the water glass is 0.5 mol / L to 1.5 mol / L; and / or, the modulus of the water glass is 2 to 4.

[0009] In some embodiments, the inorganic dispersant is added at a mass of 0.5%-1.2% of the water glass; and / or, the organic dispersant is added at a mass of 0.01%-0.5% of the water glass; the mass ratio of the inorganic dispersant to the organic dispersant is (2-7):1; and / or, the sulfate includes sodium sulfate; and / or, the sulfate includes sodium metaphosphate; and / or, the organic dispersant includes polyethylene glycol.

[0010] In some embodiments, the sodium metaphosphate comprises sodium hexametaphosphate; and / or, the mass ratio of the sulfate to the sulfate is (0.8-5):1; and / or, the average molecular weight of the polyethylene glycol is 400-4000.

[0011] In some embodiments, the heat treatment temperature is 60°C-80°C; and / or the stirring speed is 400 rpm-800 rpm; and / or the addition rate of the first mixture to the sulfuric acid solution for reaction is 3 L / h-5 L / h.

[0012] In some embodiments, the concentration of the sulfuric acid solution is 0.2 mol / L to 0.5 mol / L; and / or, the temperature of the sulfuric acid solution is 60°C to 80°C.

[0013] In some embodiments, the aging temperature is 60℃-80℃; and / or the aging time is 1h-3h; and / or, during the washing process, washing is stopped when the conductivity of the waste liquid generated by washing is <2000μs / cm.

[0014] In some embodiments, during the secondary refinement process, the first-level refinement employs a sanding process, and the second-level refinement employs an airflow atomization process.

[0015] The pressure of the airflow agitation process is 0.6MPa-1.2MPa, and the speed of the stager wheel is 10000rpm-20000rpm.

[0016] In some embodiments, the median particle size D50 of the first-stage refined silica is 5 μm-15 μm, and the median particle size D50 of the second-stage refined silica is 20 nm-4.5 μm.

[0017] Optionally, the median particle size D50 of the primary particle size of the second-stage refined silica is 20nm-60nm, and the median particle size D50 of the secondary particle size is 1.5μm-4.5μm.

[0018] Secondly, the present invention also provides silicon dioxide, which is prepared by the silicon dioxide preparation method provided in the first aspect. The silicon dioxide is ellipsoidal in shape, the median primary particle size D50 of the silicon dioxide is 20 nm-60 nm, the median secondary particle size D50 of the silicon dioxide is 1.5 μm-4.5 μm, and the specific surface area of ​​the silicon dioxide is 50 m². 2 / kg-120m 2 / kg.

[0019] Compared with the prior art, the beneficial effects of the technical solution of the present invention include:

[0020] This invention provides a method for preparing silica. By adding specific inorganic and organic dispersants to a water glass solution, the dispersion and stability of the water glass are improved, thereby regulating the reaction system of water glass added to sulfuric acid solution and inducing the formation of small silica particles with specific morphologies. Simultaneously, this invention optimizes the particle size and morphology of silica through a two-stage refining process, ultimately preparing an ellipsoidal silica suitable for precision polishing of high-hardness materials. Detailed Implementation

[0021] To facilitate understanding of the present invention, preferred embodiments are provided below to provide a more complete description of the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a thorough and complete understanding of the disclosure of the present invention.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0023] As used herein, "optional," "optional," and "optional" refer to either "with" or "without" parallel options. If multiple "optional" entries appear in a technical solution, each "optional" entry is independent unless otherwise specified and there are no contradictions or mutual constraints. The term "and / or" as used herein includes any and all combinations of one or more related listed items. Unless otherwise specified, "multiple," "multiple," etc., as used herein refer to a quantity greater than 2 or equal to 2; for example, "one or more" indicates one, two, or more than two. In open-ended technical features or solutions described herein using words such as "containing," "including," and "comprising," unless otherwise specified, additional members beyond the listed members are not excluded. This can be considered as providing both a closed-ended feature or solution consisting of the listed members and an open-ended feature or solution that includes additional members beyond the listed members.

[0024] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0025] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0026] Sapphire, due to its high hardness (up to 9 on the Mohs scale), excellent chemical stability, good thermal conductivity, and excellent optical transmittance, is widely used in LED substrates, optical windows, consumer electronics covers (such as smartphone camera covers and watch screens), and military protection. However, it is precisely these outstanding physicochemical properties, especially its extremely high hardness, that make precision polishing of sapphire an extremely difficult and critical manufacturing process. An ideal sapphire polishing process must achieve a high material removal rate (MRR) to improve production efficiency while obtaining a defect-free, low-roughness, and highly polished ultra-smooth surface. Any tiny scratch, surface damage, or subsurface damage can severely affect the performance and yield of the end product. Currently, sapphire polishing mainly employs chemical mechanical polishing (CMP) technology, the core principle of which is the synergistic effect of chemical corrosion in the polishing slurry and the mechanical abrasive action of the abrasive to achieve the preparation of an ultra-smooth surface. In this technology, the selection of the polishing abrasive is the key factor determining the polishing effect.

[0027] Silica (SiO2) is an ideal abrasive for polishing sapphire due to its moderate hardness, ability to react with the sapphire surface through chemical reactions to form a soft hydrated layer, and ease of preparation into nanoscale uniform particles. Although silica sol performs well in terms of polishing uniformity and surface finish, it has the following inherent limitations in sapphire polishing applications: (1) Silica sol has low hardness. Although its smooth spherical particle shape is beneficial for obtaining a low-damage surface, its cutting efficiency is often difficult to meet the requirements in the early stages of polishing or in situations where a high material removal rate is required; (2) High-concentration silica sol has colloidal stability issues during storage and transportation, and is prone to gelation or agglomeration, thereby affecting the product life and polishing performance consistency of the polishing slurry; (3) It is difficult to control the formulation of silica sol in polishing applications. Adding other components can easily lead to the destruction of the colloidal system, causing gelation and scrapping; (4) The film-forming characteristics of silica sol also make it difficult to clean thoroughly after polishing, affecting subsequent processes.

[0028] Therefore, the present invention aims to develop a silicon dioxide that can achieve precision polishing of the surface of high-hardness materials such as high-sapphire.

[0029] In a first aspect, the present invention provides a method for preparing silicon dioxide, comprising the following steps:

[0030] S10. Add inorganic and organic dispersants to water glass, mix, heat treat, and stir to form a first mixture; the inorganic dispersants include sulfates and phosphates.

[0031] S20. While stirring, the first mixture is added to the sulfuric acid solution in batches for reaction. When the pH of the reaction system is 2.5-3.5, the addition of the first mixture to the sulfuric acid solution is stopped, and the reaction system is aged to form a second mixture.

[0032] S30. The second mixture is subjected to solid-liquid separation and washing to form a slurry. The slurry is then refined at least in two stages to prepare silica.

[0033] This invention involves adding inorganic and organic dispersants to a water glass solution and heat-treating it to form a highly dispersed and stable mixed system. This highly dispersed and stable mixed system is then added in batches to a sulfuric acid solution for mixing. The mixing is terminated when the pH of the reaction system reaches 2.5-3.5, and silica particles are formed. During the aging process, the morphology of the silica particles is further controlled, and then they are refined in two stages to form ellipsoidal silica.

[0034] This invention employs a compound dispersant solution containing both inorganic and organic dispersants, which significantly improves the dispersibility and stability of the system during the silica reaction process. This provides a favorable system environment for silica preparation, effectively controlling the size and morphology of silica particles to obtain ellipsoidal silica particles with a narrower particle size distribution. Simultaneously, a two-stage refining process is used to optimize the particle size and morphology, jointly preparing ellipsoidal silica. The resulting silica can be used in surface polishing processes to achieve precise and efficient polishing of high-hardness material surfaces.

[0035] In some embodiments, the concentration of the water glass is 0.5 mol / L to 1.5 mol / L, including but not limited to 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L, or any of the foregoing ranges and values ​​within those ranges.

[0036] In some embodiments, the modulus of the water glass is 2-4, including but not limited to 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, or any combination thereof and values ​​within that range.

[0037] As a non-limiting example, the sulfate includes sodium sulfate, and the phosphate includes sodium metaphosphate. As a non-limiting example, the sodium metaphosphate includes sodium hexametaphosphate. This invention, by using both sulfate and phosphate as inorganic dispersants, can further improve the control of silica particle size during the reaction process. Simultaneously, the use of phosphate can also serve as a component of the polishing slurry system, thereby improving the stability and uniformity of silica in the polishing slurry, and further enhancing its polishing effect.

[0038] In some embodiments, the mass ratio of the sulfate to the phosphate is (0.8-5):1, including but not limited to 0.8:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1 or any of the foregoing ranges and values ​​within those ranges.

[0039] In some embodiments, the organic dispersant includes polyethylene glycol (PEG). The ether bonds in the PEG molecule can form hydrogen bonds with the hydroxyl groups on the surface of silica particles, thereby inducing precipitated silica to form an ellipsoidal morphology. This specific morphology of silica effectively reduces the risk of scratching the material surface during polishing and improves the precision polishing effect. Compared to spherical silica abrasives, the ellipsoidal morphology prepared by this invention provides more efficient and precise polishing.

[0040] In some embodiments, the average molecular weight of the polyethylene glycol is 400-4000; further, the average molecular weight of the polyethylene glycol is 600-2000; and even further, the average molecular weight of the polyethylene glycol is 600-800. By controlling the molecular weight of the polyethylene glycol, the dispersibility and stability of the composite dispersant can be controlled, and the content of hydrogen bonds formed between the polyethylene glycol and the hydroxyl groups on the surface of silica particles can be controlled, thereby optimizing the shape and surface morphology of the silica particles.

[0041] In some embodiments, the inorganic dispersant is added at a mass of 0.5%-1.2% of the water glass, including but not limited to 0.5%, 0.6%, 0.8%, 1%, 1.2%, or any combination thereof and values ​​within that range.

[0042] In some embodiments, the added organic dispersant is 0.01%-0.5% of the water glass, including but not limited to 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any combination thereof and values ​​within that range.

[0043] In some embodiments, the mass ratio of the inorganic dispersant to the organic dispersant is (2-7):1, including but not limited to 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or any combination thereof and values ​​within that range. This invention, by controlling the ratio of the inorganic and organic dispersants, can optimize the dispersibility and stability of water glass solutions, promote the formation of silica with specific morphologies, and simultaneously control particle size. Furthermore, the composite dispersion system formed using inorganic and organic dispersants can significantly reduce the amount of dispersant used.

[0044] In some embodiments, the heat treatment temperature is 60°C-80°C, including but not limited to 60°C, 65°C, 70°C, 75°C, 80°C, or any combination thereof and values ​​within that range. Controlling the temperature within this range controls the viscosity, dispersibility, and other properties of the solution system containing water glass and dispersant, resulting in good dispersibility and stability. Simultaneously, the temperature range also regulates the hardness and other properties of the silica particles generated in the reaction.

[0045] In some embodiments, the stirring speed is 400 rpm to 800 rpm, including but not limited to 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm or any of the foregoing ranges and values ​​within that range.

[0046] In some embodiments, the first mixture is added to the sulfuric acid solution in batches at a rate of 3 L / h to 5 L / h, including but not limited to 3 L / h, 3.5 L / h, 4 L / h, 4.5 L / h, 5 L / h, or any combination thereof and values ​​within that range. It is understood that the addition rate of the first mixture to the sulfuric acid solution is uniform. This invention controls the addition rate of the water glass mixture, thereby regulating the dispersibility and morphology of silica particles during particle formation, such as reducing particle agglomeration, while also controlling particle size and production efficiency. Adjusting the addition rate according to the composition of the water glass mixture better achieves the aforementioned technical effects.

[0047] In some embodiments, the concentration of the sulfuric acid solution is 0.2 mol / L to 0.5 mol / L, including but not limited to 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or any of the foregoing ranges and values ​​within those ranges.

[0048] In some embodiments, the temperature of the sulfuric acid solution is 60°C-80°C, including but not limited to 60°C, 65°C, 70°C, 75°C, 80°C or any combination thereof and values ​​within that range.

[0049] In some embodiments, the aging temperature is 60°C-80°C, including but not limited to 60°C, 65°C, 70°C, 75°C, 80°C or any combination thereof and values ​​within that range.

[0050] In some embodiments, the aging time is 1h-3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h or any combination thereof and values ​​within that range.

[0051] In some embodiments, the solvent used for washing includes water.

[0052] In some embodiments, washing is stopped when the conductivity of the waste liquid generated during washing is <2000 μs / cm.

[0053] In some embodiments, during the secondary refinement process, the first stage of refinement employs abrasive grinding, while the second stage employs airflow abrasive crushing. This invention further optimizes particle crushing and grading by combining abrasive grinding and airflow abrasive crushing in a dual-crushing process, resulting in a more concentrated particle size distribution and more precise particle size control in the final product.

[0054] In some embodiments, the pressure of the airflow ablation process is 0.6MPa-1.2MPa, including but not limited to 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1MPa, 1.1MPa, 1.2MPa or any of the foregoing ranges and values ​​within that range.

[0055] In some embodiments, the speed of the grading wheel is 10,000 rpm to 20,000 rpm, including but not limited to 10,000 rpm, 12,000 rpm, 14,000 rpm, 16,000 rpm, 18,000 rpm, 20,000 rpm or any of the foregoing ranges and values ​​within that range.

[0056] In some embodiments, the median particle size D50 of the first-stage refined silica is 5μm-15μm, including but not limited to 5μm, 8μm, 10μm, 12μm, 15μm or any of the foregoing ranges and values ​​within that range.

[0057] In some embodiments, the median particle size D50 of the second-stage refined silica is 20nm-4.5μm, including but not limited to 20nm, 30nm, 50nm, 80nm, 100nm, 200nm, 500nm, 800nm, 1μm, 2μm, 3μm, 4μm, 4.5μm or any of the foregoing ranges and values ​​within those ranges.

[0058] In some embodiments, the primary particle size of the second-stage refined silica is 20 nm-60 nm, and the secondary particle size is 1.5 μm-4.5 μm. Further, the primary particle size of the second-stage refined silica is 20 nm-50 nm, and the secondary particle size is 1.5 μm-3.5 μm. It is understood that both the primary and secondary particle sizes are median particle size D50.

[0059] It is understood that the particle size or median particle size mentioned in this invention are particle size dimensions measured using a laser particle size analyzer.

[0060] This invention optimizes the performance of precipitated silica as an abrasive by precisely controlling the reaction conditions during its synthesis, thereby controlling its primary particle size, morphology, aggregate structure, and particle size distribution. To eliminate potentially large, hard agglomerates, this invention also incorporates multi-stage processing techniques such as ball milling and air jet milling, significantly reducing the risk of surface scratches during polishing while maintaining excellent polishing results. Thanks to its unique structure, the precipitated silica prepared by this invention exhibits cutting force far exceeding that of traditional silica sols, achieving excellent material removal rates at low addition levels while maintaining good surface finish. Furthermore, the precipitated silica prepared by this invention exhibits high stability, no tendency to gel, and is easy to store and use. As an abrasive, it has strong compatibility in polishing slurry systems and can be further compounded with various functional additives (such as dispersants, pH adjusters, oxidants, etc.) to synergistically enhance its overall polishing performance, particularly improving cutting efficiency and surface quality. Meanwhile, the surface of precipitated silica contains abundant silanol groups (-SiOH), which are easy to modify and alter. This allows for better control over its dispersion stability in polishing fluid, its compatibility with polishing aids, and its chemical effects on the sapphire surface.

[0061] Therefore, the silica prepared by the process of the present invention is applied to the sapphire polishing process, which effectively solves the technical problems faced by existing silica sol polishing slurries and achieves efficient and high-quality polishing effect with a low-cost solution.

[0062] Secondly, the present invention also provides silicon dioxide, which is prepared by the silicon dioxide preparation method provided in the first aspect. The silicon dioxide is ellipsoidal in shape, with a primary particle size of 10 nm-100 nm, a secondary particle size of 0.5 μm-5 μm, and a specific surface area of ​​50 m². 2 / kg-120m 2 / kg. It's understandable that primary particle size refers to the diameter of the primary particles, and secondary particle size refers to the diameter of the secondary particles.

[0063] As a non-limiting example, the primary particle size includes, but is not limited to, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, or any combination thereof, and values ​​within that range. As a non-limiting example, the secondary particle size includes, but is not limited to, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or any combination thereof, and values ​​within that range. As a non-limiting example, the specific surface area includes, but is not limited to, 50 m². 2 / kg, 60m 2 / kg, 70m 2 / kg, 80m 2 / kg, 90m 2 / kg, 100m 2 / kg, 110m 2 / kg, 120m 2 / kg or any of the aforementioned ranges and values ​​within that range.

[0064] The silica prepared by this invention possesses specific shapes, sizes, and morphologies, making it suitable as an abrasive for sapphire polishing processes, significantly outperforming traditional silica sol polishing efficiency. Furthermore, the silica prepared by this invention exhibits no risk of gelation or crystallization, demonstrating excellent process stability and controllability. Due to the excellent system compatibility of the silica prepared by this invention, various functional additives can be flexibly added to the polishing slurry to further synergistically enhance the abrasive's cutting performance and surface finish. The silica prepared by this invention offers superior overall performance and significant cost-effectiveness as an abrasive system, showing broad application prospects in the field of sapphire precision polishing.

[0065] It should be noted that the experimental methods in the following embodiments of the present invention, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the embodiments are commercially available products, or can be prepared by those skilled in the art using known methods.

[0066] The specific embodiments of this invention involve the following product and reagent models and sources:

[0067] Commercially available silica sol 1: median particle size 80-120nm, pH 10, solid content 40wt%, Shandong Baite New Materials Co., Ltd.

[0068] Commercially available silica sol II: median particle size 60-80nm, pH 10, solid content 45wt%, Shandong Baite New Materials Co., Ltd.

[0069] Commercially available silica sol 3: median particle size 80-120nm, pH 10, solid content 42wt%, Guangdong Huierte Nanotechnology Co., Ltd.

[0070] Example 1

[0071] This embodiment provides silicon dioxide and its preparation method, with the following preparation process steps:

[0072] Slowly add 50g of sodium sulfate, 15g of sodium hexametaphosphate, and 10g of PEG600 to 10kg of water glass (0.7mol / L, modulus 3.2). Heat to 70℃, turn on the stirring device, and set the stirring speed of the stirring device to 500rpm to form the first mixture.

[0073] Under continuous stirring at 500 rpm, 22 L of 0.45 mol / L dilute sulfuric acid solution was added to the reactor and the temperature was raised to 70 °C.

[0074] The first mixture was slowly added to the above-mentioned 70°C dilute sulfuric acid solution at a rate of 4 L / h. When the pH value was 3.0, the addition of the first mixture was stopped, and the mixture was stirred and aged for 2 hours to form the second mixture. The second mixture was then filtered to obtain a filter cake.

[0075] The filter cake was washed multiple times by centrifugation with ultrapure water. Washing was stopped when the conductivity of the centrifugal waste liquid was less than 2000 μs / cm. The slurry was then sand-milled to obtain a silica slurry with a median particle size D50 of 10 μm. The silica slurry was then subjected to air-flow drying and crushing at a pressure of 0.8 MPa and a classifying wheel speed of 10000 rpm to obtain ellipsoidal silica with a primary particle size median particle size D50 of 35 nm and a secondary particle size median particle size D50 of 3 μm.

[0076] Example 2

[0077] This embodiment provides silicon dioxide and its preparation method, with the following preparation process steps:

[0078] Slowly add 50g of sodium sulfate, 30g of sodium hexametaphosphate, and 20g of PEG600 to 10kg of water glass (0.7mol / L, modulus 3.2). Heat to 70℃, turn on the stirring device, and set the stirring speed of the stirring device to 600rpm to form the first mixture.

[0079] Under continuous stirring at 600 rpm, 22 L of 0.45 mol / L dilute sulfuric acid solution was added to the reactor and the temperature was raised to 70 °C.

[0080] The first mixture was slowly added to the above-mentioned 70°C dilute sulfuric acid solution at a rate of 4 L / h. When the pH value was 3.0, the addition of the first mixture was stopped, and the mixture was stirred and aged for 2 hours to form the second mixture. The second mixture was then filtered to obtain a filter cake.

[0081] The filter cake was washed multiple times by centrifugation with ultrapure water. Washing was stopped when the conductivity of the centrifugal waste liquid was less than 2000 μs / cm. The slurry was then milled to obtain a silica slurry with a particle size of 10 μm. The silica slurry was then subjected to airflow drying and crushing at a pressure of 0.8 MPa and a classifier wheel speed of 15000 rpm to obtain ellipsoidal silica with a primary median particle size D50 of 20 nm and a secondary median particle size D50 of 1.5 μm.

[0082] Example 3

[0083] Slowly add 50g of sodium sulfate, 60g of sodium hexametaphosphate, and 40g of PEG600 to 10kg of water glass (0.7mol / L, modulus 3.2). Heat to 70℃, turn on the stirring device, and set the stirring speed of the stirring device to 500rpm to form the first mixture.

[0084] Under continuous stirring at 500 rpm, 22 L of 0.45 mol / L dilute sulfuric acid solution was added to the reactor and the temperature was raised to 70 °C.

[0085] The first mixture was slowly added to the above-mentioned 70°C dilute sulfuric acid solution at a rate of 4 L / h. When the pH value was 3.0, the addition of the first mixture was stopped, and the mixture was stirred and aged for 2 hours to form the second mixture. The second mixture was then filtered to obtain a filter cake.

[0086] The filter cake was washed multiple times by centrifugation with ultrapure water. Washing was stopped when the conductivity of the centrifugal waste liquid was less than 2000 μs / cm. The slurry was then milled to obtain a silica slurry with a particle size of 10 μm. The silica slurry was then subjected to airflow drying and crushing at a pressure of 0.75 MPa and a classifying wheel speed of 10000 rpm to obtain ellipsoidal silica with a primary median particle size D50 of 50 nm and a secondary median particle size D50 of 3.5 μm.

[0087] Example 4

[0088] The difference between this embodiment and Example 1 lies in the composition of the dispersant. In this embodiment, the amount of sodium sulfate added is 15g, the amount of sodium hexametaphosphate added is 4.5g, and the amount of PEG600 added is 55.5g. The remaining steps are the same as in Example 1. The silica slurry with a particle size of 10μm is obtained by sand milling. After air-drying and crushing, ellipsoidal silica with a primary particle size median D50 of 50nm and a secondary particle size median D50 of 4μm is obtained.

[0089] Example 5

[0090] The difference between this embodiment and Example 1 lies in the composition of the dispersant. In this embodiment, PEG200 is used in an equal amount to replace PEG600. The remaining steps are the same as in Example 1. The silica slurry with a particle size of 10 μm is obtained by sand milling. After air drying and crushing, ellipsoidal silica with a primary particle size median D50 of 15 nm and a secondary particle size median D50 of 1.5 μm is obtained.

[0091] Example 6

[0092] The difference between this embodiment and Example 1 lies in the composition of the dispersant. In this embodiment, the amount of sodium sulfate added is 25g, the amount of sodium hexametaphosphate added is 40g, and the amount of PEG600 added is 10g. The remaining steps are the same as in Example 1. The silica slurry with a particle size of 10μm is obtained by sand milling. After air drying and crushing, ellipsoidal silica with a primary particle size median D50 of 60nm and a secondary particle size median D50 of 4.5μm is obtained.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 lies in the composition of the dispersant. In this example, sodium hexametaphosphate is not added, and sodium sulfate is used to make up the mass. The remaining steps are the same as in Example 1. The silica slurry with a particle size of 10 μm is obtained by sand milling. After air drying and crushing, ellipsoidal silica with a primary particle size median D50 of 90 nm and a secondary particle size median D50 of 5 μm is obtained.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 lies in the composition of the dispersant. In this example, sodium sulfate is not added, and sodium hexametaphosphate is used to make up the mass. The remaining steps are the same as in Example 1. The silica slurry with a particle size of 10 μm is obtained by sand milling. After air drying and crushing, ellipsoidal silica with a primary particle size median D50 of 15 nm and a secondary particle size median D50 of 1.0 μm is obtained.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 lies in the different refining process. This comparative example does not perform sand milling; it only uses the same airflow crushing parameters as Example 1 for one refining process. The remaining steps are the same as in Example 1. After airflow drying and crushing, ellipsoidal silica with a primary median particle size D50 of 35 nm and a secondary median particle size D50 of 8 μm is obtained.

[0099] Comparative Example 4

[0100] The difference between this comparative example and Example 1 lies in the refining process. This comparative example only undergoes sand milling and does not involve airflow abrasion. The remaining steps are the same as in Example 1, resulting in ellipsoidal silica with a primary median particle size D50 of 35 nm and a secondary median particle size D50 of 10 μm.

[0101] Experimental Example 1

[0102] The silica prepared in Examples 1-6 and Comparative Examples 1-4 was formulated into a polishing slurry and its polishing performance was tested with commercially available silica sol. The specific test methods are as follows:

[0103] Preparation of polishing slurry:

[0104] According to the above-mentioned polishing solution formula, add 4.5g of sodium hydroxide and 1.5g of disodium ethylenediaminetetraacetate to 2694g of pure water under stirring. After they are completely dissolved, add 300g of abrasive and continue stirring for 30 minutes to obtain the polishing solution.

[0105] Test method:

[0106] Polishing effect tests were conducted on sapphire test blocks (30mm×30mm×10mm) using the polishing slurry prepared in the above embodiments and comparative examples, as well as three sets of commercially available silica sols. Chemical mechanical polishing was performed under the same conditions on a single-sided polishing machine using polyurethane polishing cloth. The number of test blocks in a single test was 4.

[0107] The polishing conditions were as follows: polishing liquid volume 3kg, pressure 5.75kg, large disc rotation speed 60r / min, small disc rotation speed 40r / min, flow rate mL / min, and polishing time 1h.

[0108] The polished sapphire test blocks were washed and dried, and then the surface morphology and polishing rate were measured. The specific results are shown in Table 1.

[0109] Table 1: Polishing rate and polishing effect of sapphire surface

[0110] Polishing fluid sample Removal rate (μm / h) Surface roughness (nm) Example 1 7.27 0.24 Example 2 6.78 0.19 Example 3 9.26 0.36 Example 4 10.38 0.42 Example 5 5.65 0.15 Example 6 11.01 0.59 Comparative Example 1 14.23 0.87 Comparative Example 2 4.27 0.18 Comparative Example 3 8.12 0.71 Comparative Example 4 8.31 0.84 Commercially available silica sol 4.06 0.23 Commercially available silica sol II 3.78 0.18 Commercially available silica sol 3.92 0.25

[0111] As shown in Table 1, the silica prepared by the method provided in this invention exhibits excellent polishing efficiency and rate, achieving a faster and more efficient polishing rate for sapphire surfaces compared to commercially available silica sol. Furthermore, the silica prepared in Examples 1-3 demonstrates superior overall polishing performance compared to the silica prepared in Examples 4-6, enabling better polishing of sapphire.

[0112] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0113] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing silicon dioxide, characterized in that, Includes the following steps: An inorganic dispersant and an organic dispersant are added to water glass, mixed, heat-treated, and stirred to form a first mixture; the inorganic dispersant includes sulfates and phosphates. While stirring, the first mixture is added to the sulfuric acid solution in batches to carry out the reaction. When the pH of the reaction system is 2.5-3.5, the addition of the first mixture to the sulfuric acid solution is stopped, and the reaction system is aged to form the second mixture. The second mixture is subjected to solid-liquid separation and washing to form a slurry. The slurry is then refined at least in two stages to prepare silica.

2. The method for preparing silicon dioxide according to claim 1, characterized in that, The concentration of the water glass is 0.5 mol / L to 1.5 mol / L; and / or the modulus of the water glass is 2 to 4.

3. The method for preparing silicon dioxide according to claim 1, characterized in that, The inorganic dispersant is added at a mass of 0.5%-1.2% of the water glass; and / or, the organic dispersant is added at a mass of 0.01%-0.5% of the water glass; and / or, the mass ratio of the inorganic dispersant to the organic dispersant is (2-7):1; and / or, the sulfate includes sodium sulfate; and / or, the phosphate includes sodium metaphosphate; and / or, the organic dispersant includes polyethylene glycol.

4. The method for preparing silicon dioxide according to claim 3, characterized in that, The sodium metaphosphate includes sodium hexametaphosphate; and / or, the mass ratio of the sulfate to the phosphate is (0.8-5):1; and / or, the average molecular weight of the polyethylene glycol is 400-4000.

5. The method for preparing silicon dioxide according to claim 1, characterized in that, The heat treatment temperature is 60℃-80℃; and / or the stirring speed is 400rpm-800rpm; and / or the addition rate of the first mixture to the sulfuric acid solution for reaction is 3L / h-5L / h.

6. The method for preparing silicon dioxide according to any one of claims 1 to 5, characterized in that, The concentration of the sulfuric acid solution is 0.2 mol / L to 0.5 mol / L; and / or the temperature of the sulfuric acid solution is 60°C to 80°C.

7. The method for preparing silicon dioxide according to any one of claims 1 to 5, characterized in that, The aging temperature is 60℃-80℃; and / or the aging time is 1h-3h; and / or the washing process is stopped when the conductivity of the waste liquid generated during washing is <2000μs / cm.

8. The method for preparing silicon dioxide according to any one of claims 1 to 5, characterized in that, In the secondary refinement process, the first stage of refinement uses a sandblasting process, and the second stage of refinement uses an airflow atomization process. The pressure of the airflow agitation process is 0.6MPa-1.2MPa, and the speed of the stager wheel is 10000rpm-20000rpm.

9. The method for preparing silicon dioxide according to claim 8, characterized in that, The median particle size D50 of the first-stage refined silica is 5μm-15μm, and the median particle size D50 of the second-stage refined silica is 20nm-4.5μm. Optionally, the primary particle size of the second-stage refined silica is 20nm-60nm, and the secondary particle size is 1.5μm-4.5μm.

10. Silicon dioxide, characterized in that, The silica is prepared by the silica preparation method according to any one of claims 1 to 9, wherein the silica is ellipsoidal in shape, the primary particle size of the silica is 20 nm to 60 nm, the secondary particle size of the silica is 1.5 μm to 4.5 μm, and the specific surface area of ​​the silica is 50 m². 2 / kg-120m 2 / kg.