A method for preparing a silicon dioxide powder

Abstract

The application provides a preparation method of silica powder. The method comprises the following steps: mixing and dispersing silicon powder and oxygen by carrier gas, igniting and burning to synthesize silica droplets, and sequentially cooling, separating and dedusting to obtain spherical silica powder; wherein the flow rate of the carrier gas is 0.1m 3 / h to 30m 3 / h; the flow rate of oxygen is 1m 3 / h to 250m 3 / h; and the carrier gas is one of argon, carbon dioxide, neon, helium and air. The simple process steps of the application can obtain spherical silica powder, which is beneficial to form spherical coated particles and widen the application of the spherical coated particles in the fields of aerospace, precision casting, high-voltage components, high-grade ceramics and the like.

Description

Technical Field

[0001] This application relates to the field of silica powder preparation technology, specifically to a method for preparing silica powder. Background Technology

[0002] Silica powder, due to its excellent chemical stability, thermal stability, and biocompatibility, is widely used as a filler, carrier, and additive in functional materials. Methods for preparing spherical silica powder include flame melting, sol-gel methods, and microemulsion preparation, but these processes generally suffer from high energy consumption, complex processes, high environmental costs, and uncontrollable particle morphology. With the development of materials science, the demand for efficient preparation and long-lasting use of silica materials is increasing. Problems such as poor spherical morphology, product spoilage under harsh environments, and erosion of the spherical shape affect its application in aerospace, precision casting, high-voltage components, and high-grade ceramics.

[0003] Therefore, obtaining a silica powder with a simple and efficient preparation process, good spherical morphology, and long-lasting use in harsh environments is an urgent problem to be solved. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a method for preparing silica powder, comprising the following steps: mixing and dispersing silica powder and oxygen using a carrier gas, igniting and burning to synthesize silica droplets, and sequentially cooling, separating, and removing dust to obtain spherical silica powder; The carrier gas velocity is 0.1 m. 3 / h to 30m 3 / h; oxygen flow rate 1m 3 / h to 250m 3 / h; The carrier gas is one of argon, carbon dioxide, neon, helium, or air.

[0005] Preferably, the ignition method is one of oxyhydrogen flame, plasma flame, oxyacetylene flame, or electric ignition.

[0006] Preferably, the cooling method is one of natural heat dissipation, air cooling, tank circulating cooling water, or blowing cooling air into the tank.

[0007] Preferably, the specific steps include: at a flow rate of 20m 3 / h-30m 3 Argon gas at a flow rate of 150 m / h will preheat the silicon powder and... 3 / h-250m 3 The mixture is mixed with oxygen at a concentration of / h and mechanically dispersed to obtain a mixture. The mixture is then ignited with an oxyhydrogen flame to fully combust it, resulting in silica droplets. After natural cooling, cyclone separation, and bag dust removal, the silica powder is collected into spherical particles.

[0008] Preferably, the silica powder has a 100% spherical morphology.

[0009] Preferably, the preheating temperature of the preheated silicon powder is 400-500℃.

[0010] This application describes a simple and efficient method for preparing spherical silica powder using a flame melting technique, which involves mixing a carrier gas, controlling the carrier gas flow rate and oxygen flow rate. The resulting silica powder exhibits excellent spherical morphology, which is beneficial for its applications in aerospace, precision casting, high-voltage components, and high-grade ceramics.

[0011] In some embodiments, the process further includes activating spherical silica powder and dispersing it in a chitosan solution containing silver ions, so that the silver ion-containing chitosan is deposited on the silica surface to form silver-containing chitosan-coated silica; the silver-containing chitosan-coated silica is dispersed in an organic phase containing acrylic monomers, porogens, and initiators and polymerized to coat an acrylic resin layer to obtain silica powder.

[0012] In some embodiments, the acrylic monomers are methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate.

[0013] Preferably, the mass ratio of methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate is 100:7:13-17.

[0014] This application first prepares spherical silica powder by flame melting, then coats the silica surface with a silver ion-containing chitosan layer, and further coats it with an acrylic resin layer, so that the prepared silica powder has high efficiency and long-lasting antibacterial effect, which is beneficial to its long-lasting effectiveness under harsh use conditions.

[0015] Chitosan, as a natural cationic polysaccharide, possesses good film-forming properties, biocompatibility, and certain antibacterial activity, but its antibacterial effect is relatively mild. Loading silver ions into chitosan can significantly enhance its broad-spectrum antibacterial performance. Simultaneously, chitosan acts as a chelating agent for silver ions, providing a sustained-release effect and contributing to a certain degree of sustained-release antibacterial efficacy. However, the silver-ion-containing chitosan layer directly coated on the silica surface still suffers from problems such as excessively rapid initial release of silver ions and insufficient persistence during use. Furthermore, the chitosan layer is prone to swelling and detachment in humid environments, affecting the long-term stability of the material. Additionally, the high hydrophilicity of chitosan reduces the dispersibility and compatibility of chitosan-coated silica in organic matrices, thus affecting material performance and bulk antibacterial properties.

[0016] Chitosan molecules contain multiple amino and hydroxyl groups. In weak acids, they can form a positive charge, adsorbing the negatively charged components of bacterial cell walls, disrupting the cell membrane, and entering the cell to disrupt cell synthesis. They can also chelate trace metal ions, inhibiting bacterial growth activity. Therefore, chitosan itself possesses certain antibacterial properties. Furthermore, chitosan can bond well with activated silica, forming a stable coating film on its surface. This facilitates the formation of a sustained-release layer for silver ions. Silver ions are broad-spectrum, highly effective antibacterial agents that can bind to proteins, inactivating enzymes, interfering with DNA replication, and attacking cell membrane lipids, causing oxidative damage. By loading silver ions into chitosan to achieve silica coating, the chelating ability of the amino and hydroxyl groups on the chitosan molecular chain anchors silver ions at a high concentration at the bacterial contact interface, forming a localized high-concentration bactericidal zone. Both target cells simultaneously, and chitosan also acts as a carrier to control the release rate of silver ions, achieving long-lasting antibacterial effects. Therefore, this method enhances the antibacterial properties and sustained-release antibacterial effect of silica powder to a certain extent.

[0017] However, the release of silver ions from the chitosan layer containing silver ions directly coated on the silica surface is too rapid and lacks persistence. Furthermore, the chitosan layer is prone to swelling and detachment, affecting the long-term stability of the material. Its compatibility with organic matrices is also poor, impacting material performance and the effectiveness of its bulk antibacterial properties. Based on this, the inventors considered further coating the surface with a specific organic acrylic resin, selecting methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate as the acrylic monomers. This not only solved the compatibility problem but also significantly improved the bulk and long-lasting antibacterial properties of silica. Analysis suggests that while acrylic resin coating significantly improves compatibility, it further presents problems such as chitosan's inability to contact bacteria and difficulty in releasing silver ions. This application first selects methyl methacrylate as the base monomer and, in conjunction with a porogen, obtains a porous acrylic resin layer on the chitosan layer surface. This multi-layered structure not only improves powder compatibility but also further enhances the sustained release of silver ions based on the coating layer. The porous structure ensures that chitosan contacts bacteria, thus successfully achieving synergistic antibacterial effects of silver ions and chitosan. Furthermore, acrylic acid, imidazole ethyl methacrylate, and methyl methacrylate are added for copolymerization. The imidazole ring of imidazole ethyl methacrylate itself has excellent antibacterial properties. Based on cell membrane disruption, bioinhibition, and synergistic effects with silver-containing chitosan, it can further enrich the antibacterial mechanism and achieve synergistic antibacterial effects. In addition, the imidazole ring has a complexing effect on silver ions. When silver ions are slowly released from the chitosan layer, the imidazole ring on the pore surface of the acrylic resin and the outer surface of the shell can complex silver ions, thereby achieving the retention of silver ions and delaying their loss. On the pore surface, chitosan, imidazole, and silver ions synergistically inhibit antibacterial activity, while on the outer surface of the shell, silver ions and imidazole synergistically inhibit antibacterial activity, thus effectively prolonging the antibacterial effect of silica. The acrylic acid groups of acrylic acid monomers can also complex and slowly release silver ions, aiding in long-lasting antibacterial activity. Individual carboxyl groups or imidazoles are monodentate ligands, which are relatively unstable when complexing with silver ions and easily dissociate. When both carboxyl and imidazole are present, they can form a synergistic chelate with silver ions, resulting in a more stable chelate ring. The carboxyl group assists in coordination, further enhancing complexation stability through the interaction of the negative charge of the carboxylate group and silver ions. It can also attract anions to the coordination sites of imidazole, thereby achieving effective and long-lasting retention of silver ions and further enhancing slow release. On the other hand, the carboxyl groups provided by acrylic acid monomers and the amino groups provided by imidazole can interact with chitosan, significantly improving the tightness of the acrylic resin coating layer. The combination of acrylic acid and methyl methacrylate (MMA) soft and hard monomers allows for better coating of imidazole-containing acrylic resin on the chitosan layer surface, thus contributing to the long-lasting antibacterial properties and stability of the silica particles.

[0018] Therefore, this application coats the surface of the silver-containing chitosan layer with the aforementioned specific imidazole-containing acrylic resin. Combined with the porous structure and the selection of acrylic monomers, this achieves durable, stable, and highly effective antibacterial properties of the silica particles. Furthermore, the three monomers within the aforementioned range maintain better stability of the acrylic resin layer, complex silver ions, and synergistic antibacterial effectiveness, further optimizing the durable antibacterial performance.

[0019] In some embodiments, the porogen is polyethylene glycol with a molecular weight of 4000-10000 Da.

[0020] Polyethylene glycol (PEG) participation in polymerization can form a porous structure in the acrylic resin layer, achieving an unexpected and sustained improvement in antibacterial properties within the molecular scope of this application. This may be because if the molecular weight of PEG is too small, the pore size is relatively small, the release of silver ions is too slow, the instantaneous antibacterial effect is insufficient, and it affects the contact between chitosan and bacteria, which is not conducive to achieving sustained synergistic antibacterial activity. On the other hand, if the molecular weight of PEG is too large, the pore size is relatively large, which can easily degrade the effect of the acrylic resin layer in enhancing the slow release, and the contact between silver ions and imidazole and carboxyl groups in the acrylic resin is reduced, thus not conducive to sustained antibacterial activity.

[0021] In some implementations, the specific steps include: at a flow rate of 20m 3 / h-30m 3 Argon gas at a flow rate of 150 m / h will preheat the silicon powder and... 3 / h-250m 3 / h of oxygen is mixed and mechanically dispersed to obtain a mixture; the mixture is then ignited with an oxyhydrogen flame to fully combust it to obtain silica droplets, which are then naturally cooled, separated by cyclone separation, and collected by bag dust removal to obtain spherical silica powder. Spherical silica powder is dispersed in an acidic solution, a silane coupling agent is added and heated to react, followed by centrifugation, washing with water, and drying to obtain activated silica; chitosan is dissolved in acetic acid solution, and silver salt is added and stirred to obtain a chitosan solution containing silver ions; the activated silica is dispersed in the chitosan solution containing silver ions and reacted for 2-5 hours, followed by centrifugation, washing, and drying to obtain silver-coated chitosan silica. An organic phase is obtained by dispersing acrylic monomers, porogens, and initiators in acetone; silver-containing chitosan-coated silica is dispersed in the organic phase, and after heating and reacting for 6-10 hours, silica powder is obtained.

[0022] In some embodiments, the mass ratio of the acrylic monomer, porogen, and initiator is 100:25:0.5-1.5.

[0023] Compared with the prior art, the beneficial effects of this application are at least as follows: 1. This application provides an efficient and simple process for preparing spherical silica, which produces silica spheres with good morphology, thus broadening its application scenarios.

[0024] 2. This application effectively enhances the sustained release of silver ions by sequentially coating a silver-containing chitosan layer and an acrylic resin layer onto the surface of silica, achieving a synergistic antibacterial effect of silver ions and chitosan. The acrylic monomers selected are methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate, further enriching the antibacterial mechanism and pathway, improving antibacterial activity, and achieving a significant improvement in long-lasting and highly effective antibacterial properties based on the effects of imidazole and acrylic acid. Further limiting the content of these three monomers optimizes the long-lasting antibacterial effect.

[0025] 3. This application defines a specific molecular weight range for the porogen polyethylene glycol. Based on pore size release, chitosan contact area, and the complexing effect of imidazole and acrylic acid with silver ions, a molecular weight within the range specified in this application was selected to achieve further optimized and durable antibacterial properties. Detailed Implementation

[0026] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0027] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0029] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0030] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0031] 600 mesh silica powder; chitosan purchased from Zhejiang Yicun Biotechnology Co., Ltd., with 99% effective ingredients. Example 1

[0032] S1: Through a flow velocity of 30m 3 An argon carrier gas flow rate of / h preheats silicon powder to 500°C and a flow rate of 200m / h. 3 The mixture is prepared by mixing oxygen at a rate of / h and mechanically dispersing it to obtain a mixture. The molar ratio of silicon powder to oxygen is controlled at 1:1.2. The mixture is then ignited with an oxyhydrogen flame to ensure complete combustion. The oxygen flow rate is adjusted to ensure the temperature is between 1800-1900℃. The mixture is kept at this temperature for 2.5h to obtain silicon dioxide droplets. After natural cooling, cyclone separation, and bag dust removal, spherical silicon dioxide powder is collected. S2: 10 parts by mass of spherical silica powder were dispersed in 100 parts by mass of an acetate-sodium acetate buffer solution with pH 4.5. 0.2 parts by mass of silane coupling agent KH550 were added, and the mixture was heated to 45°C and reacted for 2 hours. After centrifugation, washing with water 3 times, and drying, activated silica was obtained. 1.5 parts by mass of chitosan were dissolved in 100 parts by mass of a 1.5 wt% acetic acid solution. 0.2 g of silver nitrate was added and stirred for 1 hour to obtain a chitosan solution containing silver ions. The activated silica was dispersed in the chitosan solution containing silver ions and reacted at room temperature for 4 hours. After centrifugation, washing with water 3 times, and vacuum drying, silver-coated chitosan silica was obtained. S3: 5 parts by mass of acrylic monomer, 1.25 parts by mass of porogen, and 0.05 parts by mass of initiator azobisisobutyronitrile are dispersed in 80 parts by mass of acetone to obtain an organic phase; the silver-containing chitosan-coated silica obtained in S2 is dispersed in the organic phase, heated to 75°C and refluxed for 8 hours, then centrifuged, washed with ethanol, and vacuum dried to obtain silica powder; The acrylic monomers are methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate in a mass ratio of 100:7:15; The pore-forming agent is polyethylene glycol with a molecular weight of 6000 Da. Example 2

[0033] The only difference between Example 2 and Example 1 is that the acrylic monomer is methyl methacrylate and acrylic acid in a mass ratio of 100:22. Example 3

[0034] The only difference between Example 3 and Example 1 is that the acrylic monomers are methyl methacrylate and imidazole ethyl methacrylate in a mass ratio of 100:22. Example 4

[0035] The only difference between Example 4 and Example 1 is that the acrylic monomer is methyl methacrylate. Example 5

[0036] The only difference between Example 5 and Example 1 is that the polyethylene glycol has a molecular weight of 1000 Da. Example 6

[0037] The only difference between Example 6 and Example 1 is that the molecular weight of polyethylene glycol is 20,000 Da.

[0038] Comparative Example 1 S1: Through a flow velocity of 30m 3 An argon carrier gas flow rate of / h preheats silicon powder to 500°C and a flow rate of 200m / h. 3 The mixture is prepared by mixing oxygen at a rate of / h and mechanically dispersing it to obtain a mixture. The molar ratio of silicon powder to oxygen is controlled at 1:1.2. The mixture is then ignited with an oxyhydrogen flame to ensure complete combustion. The oxygen flow rate is adjusted to ensure the temperature is between 1800-1900℃. The mixture is kept at this temperature for 2.5h to obtain silicon dioxide droplets. After natural cooling, cyclone separation, and bag dust removal, spherical silicon dioxide powder is collected. S2: Disperse 10 parts by mass of spherical silica powder in 100 parts by mass of a pH 4.5 sodium acetate buffer solution, add 0.2 parts by mass of silane coupling agent KH550, heat to 45℃ and react for 2 hours, centrifuge, wash with water 3 times, and dry to obtain activated silica; dissolve 1.5 parts by mass of chitosan in 100 parts by mass of a 1.5 wt% acetic acid solution, add 0.2 g of silver nitrate and stir for 1 hour to obtain a chitosan solution containing silver ions; disperse the activated silica in the chitosan solution containing silver ions and react at room temperature for 4 hours, centrifuge, wash with water 3 times, and vacuum dry to obtain silver-containing chitosan-coated silica, i.e., silica powder; Test section The silica powders obtained in the examples and comparative examples of this application were subjected to antibacterial tests. Referring to the test method (GB / T 21510-2008)-A, the antibacterial rate I of the standard bacterial strains *Escherichia coli* 8099 and *Staphylococcus aureus* ATCC6538 was tested. The silica powder samples obtained in the examples and comparative examples were placed at 55°C and 50% humidity for 90 days, and the antibacterial rate II was tested. The percentage decrease in antibacterial rate was calculated as (antibacterial rate I - antibacterial rate II) / antibacterial rate I * 100%. The test results are shown in Table 1. Table 1

[0039] According to Table 1, Examples 1-6 and Comparative Example 1 all exhibited good initial antibacterial properties. Example 1, compared to Examples 2 and 4 and Comparative Example 1, demonstrated superior antibacterial properties, which is beneficial for improving its usability under harsh environments. The imidazole structure in the acrylic resin is beneficial for further enhancing the synergistic antibacterial performance of chitosan and silver ions. Examples 1 and 5-6 show that the porous structure of the acrylic resin layer affected the initial antibacterial properties; excessively small pore sizes are not conducive to achieving a synergistic antibacterial effect. The decreasing trend in antibacterial rate observed in Examples 1-6 and Comparative Example 1 indicates that coating with acrylic resin can improve the long-lasting antibacterial effect. Examples 1-4 show that Example 1 significantly improved the long-lasting antibacterial properties of silica through the combined action of three monomers: methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate. Combined with Examples 1 and 5-6, it can be seen that more optimized long-lasting antibacterial performance can be achieved within the molecular weight range of polyethylene glycol in this application.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application.

Claims

1. A method for preparing silica powder, characterized in that, Includes the following steps: Silicon powder and oxygen are mixed and dispersed by a carrier gas, ignited and burned to synthesize silicon dioxide droplets, and then cooled, separated and dust-removed in sequence to obtain spherical silicon dioxide powder. The carrier gas velocity is 0.1 m. 3 / h to 30m 3 / h; oxygen flow rate 1m 3 / h to 250m 3 / h; The carrier gas is one of argon, carbon dioxide, neon, helium, or air.

2. The preparation method according to claim 1, characterized in that, The ignition method is one of the following: hydrogen-oxygen flame, plasma flame, oxyacetylene flame, or electric ignition.

3. The preparation method according to claim 1, characterized in that, The cooling method is one of natural heat dissipation, air cooling, tank circulating cooling water, or blowing cooling air into the tank.

4. The preparation method according to claim 1, characterized in that, Specifically, the steps include: at a flow rate of 20m... 3 / h-30m 3 Argon gas at a flow rate of 150 m / h will preheat the silicon powder and... 3 / h-250m 3 The mixture is mixed with oxygen at a concentration of / h and mechanically dispersed to obtain a mixture. The mixture is then ignited with an oxyhydrogen flame to fully combust it, resulting in silica droplets. After natural cooling, cyclone separation, and bag dust removal, the silica powder is collected into spherical particles.

5. The preparation method according to claim 1, characterized in that, The silica powder has a 100% spherical morphology.

6. The preparation method according to claim 4, characterized in that, The preheating temperature of the preheated silicon powder is 400-500℃.

7. The preparation method according to claim 1, characterized in that, The method also includes the following steps: activating spherical silica powder and dispersing it in a chitosan solution containing silver ions, so that the silver ion-containing chitosan is deposited on the silica surface to form silver-containing chitosan-coated silica; dispersing the silver-containing chitosan-coated silica in an organic phase containing acrylic monomers, a porogen, and an initiator, polymerizing and coating an acrylic resin layer to obtain silica powder; wherein the acrylic monomers are methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate; the mass ratio of methyl methacrylate, acrylic acid, and imidazole ethyl methacrylate is 100:7:13-17; the porogen is polyethylene glycol with a molecular weight of 4000-10000 Da.

8. The preparation method according to claim 7, characterized in that, The preparation method specifically includes the following steps: dispersing spherical silica powder in an acidic solution, adding a silane coupling agent and heating to react, centrifuging, washing with water, and drying to obtain activated silica; dissolving chitosan in an acetic acid solution, adding silver salt and stirring to obtain a chitosan solution containing silver ions; dispersing the activated silica in the chitosan solution containing silver ions and reacting for 2-5 hours, centrifuging, washing, and drying to obtain silver-containing chitosan-coated silica.

9. The preparation method according to claim 7, characterized in that, The process also includes the following steps: dispersing acrylic monomers, porogens, and initiators in acetone to obtain an organic phase; dispersing silver-containing chitosan-coated silica in the organic phase; heating and reacting for 6-10 hours; and then processing to obtain silica powder.

10. The preparation method according to claim 9, characterized in that, The mass ratio of the acrylic monomer, porogen, and initiator is 100:25:0.5-1.5.

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