Spherical silicon dioxide micro powder with controllable particle size as well as preparation method and application of spherical silicon dioxide micro powder

Abstract

The invention provides spherical silicon dioxide micropowder with a controllable particle size and a preparation method and application thereof. The preparation method comprises the following steps: mixing a sodium silicate solution and an ethanol dispersion liquid in proportion, uniformly stirring to obtain a mixed solution I, adding an ammonia water solution into the mixed solution I, and uniformly stirring to obtain a mixed solution II; heating and stirring the mixed solution II, adding an acid solution after a set temperature is reached, and reacting to obtain a turbid liquid A; keeping heating and stirring states, and simultaneously injecting a sodium silicate solution and an acid solution to react to obtain a turbid liquid B; aging the turbid liquid B to obtain turbid liquid C; dehydrating, washing and drying the turbid liquid C to obtain spherical silicon dioxide micro powder A with a controllable particle size, and densifying the spherical silicon dioxide micro powder A to obtain spherical silicon dioxide micro powder B; according to the method, the particle size within the range of 0.2-3 microns can be accurately controlled, secondary nucleation is effectively inhibited, and the prepared spherical silicon dioxide micro powder has the characteristics of excellent monodispersity, high sphericity degree, good purity and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic material preparation, in particular to a spherical silica micro-powder with controllable particle size, a preparation method and application thereof. BACKGROUND

[0002] Spherical silica micro-powder is widely used in electronic packaging, precision polishing, chromatographic packing, high-end coatings and cosmetics, etc. due to its high chemical stability, good dispersibility, excellent mechanical properties and thermal stability. In these applications, the particle size, particle size distribution (monodispersity), sphericity and surface properties of the material are key factors determining its final performance.

[0003] Currently, the classical methods for preparing spherical silica micro-powder mainly include sol-gel method (Stöber method) and microemulsion method, etc. Among them, the Stöber method is widely concerned due to its relatively simple process and good product sphericity. This method usually prepares monodisperse silica microspheres through hydrolysis and polycondensation of silicate precursors (such as tetraethyl orthosilicate, TEOS) in a mixed system of alcohol, water and ammonia. However, the traditional Stöber method and its modified processes have significant limitations. First, the controllable particle size range is usually narrow, and it is difficult to realize continuous and controllable preparation from hundreds of nanometers to several microns while ensuring monodispersity. Second, this method usually uses one-time feeding or single titration, and when growing larger particle size particles, the reaction system is prone to homogeneous nucleation (i.e. secondary nucleation), resulting in the appearance of new small particles in the final product, thus widening the particle size distribution (PDI) and deteriorating the monodispersity. Finally, using TEOS and other silicates as precursors, the raw material cost is high, which is not conducive to large-scale industrial production.

[0004] To overcome the above-mentioned shortcomings, the "seed growth method" emerged as the times require. This strategy aims to first prepare monodisperse silica "seeds", and then use these seeds as cores to uniformly deposit new silica sources on the seed surface by precisely controlling the reaction conditions, so as to realize the amplification of particle size. However, the existing seed growth technology still faces severe challenges. The main technical problems are as follows: First, the size control accuracy of spherical particles is poor. The core of the growth process is to ensure that the reaction system is always in a state of "growth priority, nucleation inhibition". If the reactants are added too fast or the local concentration is uneven, the concentration of active monomers (such as silicic acid) in the system will exceed the critical concentration of secondary nucleation, thereby initiating new nucleation, destroying the monodispersity and uniformity of particle size of the product. Secondly, the process stability and controllability are poor. The traditional single-path titration method is difficult to accurately maintain the dynamic balance of the reaction system. The pH value of the reaction system will fluctuate during the titration process, and the pH value directly affects the condensation rate of silicic acid, and its fluctuation will directly lead to uneven growth rate, and even change the reaction path. At the same time, the lack of precise control of the quantitative relationship between the amount of reactants added and the final particle size makes the controllability of the particle size largely dependent on experience, and the repeatability and predictability are poor.

[0005] Therefore, conquering a method for preparing spherical silica micro-powder which can realize wide range, high precision particle size control, and completely inhibit secondary nucleation, and ensure that the product has excellent monodispersity, has important significance for meeting the harsh requirements of high-end application fields on material performance, and promoting its industrial production. SUMMARY

[0006] The present application aims to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present application is to provide a method for preparing spherical silica micro-powder with controllable particle size; the second purpose of the present application is to provide a spherical silica micro-powder with controllable particle size; the third purpose of the present application is to provide an application of a spherical silica micro-powder with controllable particle size.

[0007] In order to achieve the above-mentioned purposes, one aspect of the present application provides a method for preparing spherical silica micro-powder with controllable particle size, which comprises: 1) mixing sodium silicate solution and ethanol dispersion liquid in proportion, and stirring uniformly to obtain mixed liquid I, adding ammonia solution to the mixed liquid I and stirring uniformly to obtain mixed liquid II; 2) heating and stirring the mixed liquid II, adding acid solution after reaching the set temperature, and reacting to obtain suspension A; 3) while maintaining the heating and stirring state of the suspension A, simultaneously injecting sodium silicate solution and acid solution to react, maintaining the pH constant during the reaction process, and obtaining suspension B after the reaction is completed; 4) aging treatment is performed on the suspension B to obtain suspension C; 5) Dehydrate, rinse and dry the suspension C to obtain the spherical silica powder A with controllable particle size.

[0008] Alternatively, the mass percentage concentration of the sodium silicate solution in step 1) is 5% to 10%; the ethanol dispersion solution is a mixed solution of anhydrous ethanol and water, wherein the volume ratio of anhydrous ethanol to water is 1:1.5 to 1:2.5; the ratio is volume ratio, the volume ratio is 1:3 to 1:6; the sodium silicate concentration in the mixed solution I is 0.2 to 0.4 mol / L; the ammonia solution is concentrated ammonia water with NH3 content of 25% to 28%, the volume ratio of the addition amount of the ammonia solution to the mixed solution I is 1:20 to 1:30; the uniform stirring is carried out in an acid and alkali resistant reaction kettle with stirring and heating device, the stirring speed of the uniform stirring is 100 to 500 r / min, and the stirring time is 20 to 60 min.

[0009] Alternatively, the stirring speed of the heating and stirring in step 2) is 100 to 500 r / min, and the set temperature is 30 to 60℃; the adding of the acid solution refers to spraying the acid solution into the mixed solution II through a solution pressure pump during stirring; the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, citric acid and ascorbic acid solution, the H + concentration in the acid solution is 0.5 to 3 mol / L; the adding speed of the acid solution is 500 to 2000 mL / (min·m 2 ); the heating and stirring time is 2 to 4 h; the pH value of the suspension A is 10 to 10.5, the particle size of the particles in the suspension A is 0.1 to 0.2 μm, and the particle size distribution PDI is less than 0.1.

[0010] Alternatively, in step 3), the simultaneous injection of the sodium silicate solution and the acid solution is carried out by using a double feeding system, the double feeding system includes two independent solution pressure pumps and corresponding feeding spray ports, the two feeding spray ports are symmetrically distributed on the inner side wall of the reaction kettle, and the feeding direction forms an angle of 30° to 60° with the rotation direction of the fluid generated by stirring in the reaction kettle; the two independent feeding spray ports are used to simultaneously inject the suspension A; in step 3), the concentration of the sodium silicate solution is 0.2 to 0.5 mol / L, the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, citric acid and ascorbic acid solution, the H + concentration in the acid solution is 0.5 to 2 mol / L; the molar ratio of the feeding of the sodium silicate solution and the acid solution is 1:1.8 to 1:2.2 when they are simultaneously injected, the feeding speed ratio of the sodium silicate solution and the acid solution is 1:1.2 to 1:2.5, and the injection speed of the sodium silicate solution is 300 to 1500 mL / (min m²).

[0011] Alternatively, the amount of sodium silicate solution added is calculated by formula (1): (1) wherein V add is the amount of sodium silicate solution added, in L; R target is the particle size of the product, in m; R seed is the particle size of the particles in the suspension A, in m; p is the density of silicon dioxide, in kg / m 3 ; M SiO2 is the molar mass of silicon dioxide, with a value of 0.06008 kg / mol; N A is the Avogadro constant, with a value of 6.022·10 23 mol -1 ; and C is the concentration of sodium silicate, in mol / L.

[0012] Alternatively, the heating and stirring state in step 3) is maintained at the heating temperature and stirring speed in step 2); the pH is kept constant, meaning that the pH value maintained by the double-feeding system is stably controlled at 10-10.5, with a pH fluctuation range of <±0.2; and the reaction time is 4-8 h.

[0013] Alternatively, the aging treatment in step 4) is a standing and aging process for the suspension B, and the temperature of the aging treatment is 25-60°C, and the time is 4-24 h.

[0014] Alternatively, the dehydration in step 5) is a dehydration process for the suspension C using a dehydration machine with a flushing device, and the dehydration machine includes one of a filter press, a suction filter and a centrifuge, and the water content of the product after dehydration is 30%-60%; the flushing is washing 2-5 times using an ethanol solution with a concentration of 50%-80% on the basis of dehydration, so that the content of sodium salt in the residual solution after flushing is less than 0.05-0.1 mmol / g; the drying mode includes one of vacuum drying, hot air drying or freeze drying; the conditions for vacuum drying are: a vacuum degree of 0.08-0.1 MPa, a temperature of 80-120°C, and a time of 6-10 h; the conditions for hot air drying are: a temperature of 100-150°C, an air speed of 0.5-1.5 m / s, and a time of 4-8 h; and the conditions for freeze drying are: a temperature of -50°C to -30°C, and a time of 12-48 h.

[0015] Alternatively, the preparation method further includes a densification treatment for the spherical silicon dioxide micro-powder A with controllable particle size obtained in step 5) to obtain spherical silicon dioxide micro-powder B with controllable particle size.

[0016] Optionally, the densification treatment is high-temperature treatment of the particle-size-controllable spherical silica micro-powder A by using a fluidized bed calcination system; the fluidized bed calcination system comprises a fluidized gas supply unit, a gas preheating unit, a fluidized bed reactor and a gas-solid separation unit; the fluidized gas is one of air or nitrogen; the gas velocity of the fluidized gas is 0.1-0.5 m / s; the temperature of the densification treatment is 500-800 ℃, and the time is 1-4 h.

[0017] Another aspect of the present application provides a particle-size-controllable spherical silica micro-powder, which can be prepared by the above-mentioned method for preparing a particle-size-controllable spherical silica micro-powder, and comprises particle-size-controllable spherical silica micro-powder A and particle-size-controllable spherical silica micro-powder B.

[0018] Optionally, the particle-size-controllable spherical silica micro-powder A has a particle size controllable range of 0.2-3 μm, excellent monodispersity (PDI < 0.1), an amorphous phase, a dispersed spherical microscopic morphology, a whiteness > 95%, a sphericity > 0.95 and a spheroidization rate > 98%.

[0019] Optionally, the particle-size-controllable spherical silica micro-powder B has a wide particle size controllable range of 0.2-3 μm, excellent monodispersity (PDI < 0.1), an amorphous phase, a dispersed spherical microscopic morphology, a whiteness > 95%, a sphericity > 0.95, a spheroidization rate > 98%, a water content < 0.05%, a tap density of 0.4-0.7 g / cm 3 , and a weight loss < 0.5% at 950 ℃ by thermogravimetric analysis.

[0020] Still another aspect of the present application provides an application of a particle-size-controllable spherical silica micro-powder, which comprises particle-size-controllable spherical silica micro-powder A and particle-size-controllable spherical silica micro-powder B.

[0021] Optionally, the particle-size-controllable spherical silica micro-powder A is suitable for general fields with relatively low requirements for hardness and thermal stability: when the particle size is 0.2-1 μm, it is suitable for use as a catalyst carrier, a drug carrier and a high-efficiency adsorbent; when the particle size is 1-3 μm, it is suitable for use as a light scattering agent for high-end cosmetics, a paint matte agent and a light filler for high polymer materials.

[0022] Alternatively, the particle size controllable spherical silica powder B is suitable for high-end and precision fields: when the particle size is 0.2-1 μm, it is suitable for high-density filling of epoxy plastic encapsulating material for electronic packaging, key abrasive of semiconductor wafer chemical mechanical polishing slurry and heat-conducting enhancement filler of heat-conducting silicone grease; when the particle size is 1-3 μm, it is suitable for chromatographic column filler of high-performance liquid chromatography, scratch-free polishing material of precision ceramic or metal device, and functional skin feel regulator of high-end cosmetics.

[0023] Compared with the prior art, the beneficial effects of the present application include at least one of the following: (1) In the preparation method, the present application breaks through the technical bottleneck that the traditional method is difficult to balance accurate control and excellent monodispersity in a wide particle size range by means of "seed growth based on quantitative calculation" and "double feeding-constant pH control" dual technologies, realizes linear and predictable regulation of product particle size from 0.2 μm to 3 μm, and completely suppresses secondary nucleation, while using cheap sodium silicate as raw material, significantly reducing the cost, high process stability, and easy to scale production.

[0024] (2) In the product performance, due to the accurate control of the above method, the obtained spherical silica powder presents extremely excellent monodispersity (PDI < 0.1), perfect spherical morphology (sphericity > 0.95, spheroidization rate > 98%), and can provide basic and densified high-performance specifications, the latter has low water content and high thermal stability, and the comprehensive performance meets the top application requirements.

[0025] (3) In the product application, the product realizes the localization breakthrough in high-end application fields, its precisely matched particle size and performance spectrum can meet the needs of semiconductor CMP polishing, high-end epoxy plastic encapsulating material, high-performance chromatographic filler and other harsh scenes, successfully promoting the leap from general filler to key functional materials in specific scenes, and providing a full series of professional solutions for downstream industries.

[0026] (4) In the process control, the present application verifies and optimizes the calculation formula (formula (1)) of the amount of sodium silicate added through a large number of experimental data, which establishes an accurate and quantifiable mathematical relationship between the amount of reactants added and the particle size of the target product. The introduction of this empirical formula changes the particle size control from traditional empirical groping to predictable and calculable accurate engineering, significantly reducing the repeated trial and error required to adjust the particle size in research and production, greatly improving the stability, repeatability and production efficiency of the process. BRIEF DESCRIPTION OF DRAWINGS

[0027] The above and other objects and / or characteristics of the present application will become more apparent from the following description, taken in conjunction with the accompanying drawings, in which: Figure 1A process flow diagram of the preparation method of the present application is shown.

[0028] Figure 2 A microscopic morphology diagram of the spherical silica micro powder prepared in Example 1 of the present application is shown.

[0029] Figure 3 A microscopic morphology diagram of the spherical silica micro powder prepared in Example 2 of the present application is shown.

[0030] Figure 4 A microscopic morphology diagram of the spherical silica micro powder prepared in Example 3 of the present application is shown.

[0031] Figure 5 A particle size distribution diagram of the spherical silica micro powder prepared in Example 1 of the present application is shown.

[0032] Figure 6 A particle size distribution diagram of the spherical silica micro powder prepared in Example 2 of the present application is shown.

[0033] Figure 7 A particle size distribution diagram of the spherical silica micro powder prepared in Example 3 of the present application is shown.

[0034] Figure 8 A microscopic morphology diagram of the spherical silica micro powder prepared in Comparative Example 1 of the present application is shown. DETAILED DESCRIPTION

[0035] Hereinafter, a particle size controllable spherical silica micro powder, a preparation method thereof and applications thereof will be described in detail in conjunction with exemplary embodiments.

[0036] The present application provides a continuous and controllable preparation method of monodisperse and high-sphericity silica micro powder by seed growth method combined with precise pH control and feeding technology, and high-performance spherical silica micro powder prepared thereby and applications thereof in various fields. The present application overcomes the defects of narrow controllable particle size range, poor monodispersity due to secondary nucleation, poor process stability and repeatability, and high cost in the preparation of spherical silica micro powder by traditional stober method and existing seed method. Specifically, one of the purposes of the present application is to provide a preparation method for continuously and accurately controlling the particle size in the range of 0.2 μm to 3 μm using inexpensive sodium silicate as raw material. Another purpose of the present application is to ensure complete inhibition of secondary nucleation during particle growth by innovative process control strategy, thereby obtaining spherical silica micro powder with extremely excellent monodispersity (PDI < 0.1). Still another purpose of the present application is to provide a preparation process with accurate process parameters, good stability, high repeatability and suitability for large-scale production.

[0037] The key feature of this invention's method for preparing spherical silica micropowder with controllable particle size lies in its core technical approach, which combines a "seed growth method" with "dual-feed constant pH control." This approach achieves linear, continuous, and predictable control over the product particle size from the nanometer to the micrometer scale, while completely suppressing secondary nucleation and ensuring the monodispersity and uniformity of the product. The resulting product exhibits excellent performance and can meet the particle size requirements of various fields.

[0038] Exemplary Example 1 This exemplary embodiment provides a method for preparing spherical silica micropowder with controllable particle size, such as... Figure 1 The schematic diagram of the process flow shows that the preparation method can be briefly described as follows: Sodium silicate solution, ethanol dispersion, and ammonia solution are mixed and heated with stirring. An acid solution is then added to react and obtain a suspension. Sodium silicate solution and acid solution are then simultaneously injected into the suspension to continue the reaction. After growth and aging, the mixture is washed and dehydrated to obtain a filter cake and filtrate. The dried filter cake yields spherical silica powder A. Spherical silica powder A is calcined to obtain spherical silica powder B. Furthermore, the filtrate can be post-treated to obtain silica and sodium chloride.

[0039] Specifically, the preparation method described in this exemplary embodiment may include: S1. Mix sodium silicate solution and ethanol dispersion in a certain proportion to obtain mixture I. Add ammonia solution to mixture I and stir until homogeneous to obtain mixture II.

[0040] In this embodiment, the mass percentage concentration of the sodium silicate solution is 5%~10%, such as 5.1%, 8%, and 9.9%. If the mass percentage of the sodium silicate solution is too low, the silicon source concentration in the reaction system is insufficient, resulting in too few crystal nuclei generated per unit volume. This not only reduces production efficiency but also leads to excessively large interparticle spacing in the subsequent growth stage, making it difficult to effectively suppress secondary nucleation and ultimately failing to obtain seeds with excellent monodispersity (PDI<0.1). If the mass percentage of the sodium silicate solution is too high, the supersaturation of the reaction system will reach its peak instantaneously, triggering explosive homogeneous nucleation. This rapid and uncontrollable nucleation process generates a large number of small, non-uniform crystal nuclei, which are prone to heterogeneous aggregation and agglomeration between particles, resulting in a significantly widened seed particle size distribution (PDI>0.2), thus completely undermining the basis for subsequent precise particle size control.

[0041] In this embodiment, the ethanol dispersion is a mixed solution of anhydrous ethanol and water, wherein the volume ratio of anhydrous ethanol to water is 1:1.5 to 1:2.5, such as 1:1.51, 1:2, and 1:2.49. Ethanol plays two key roles in this system. First, as a dispersion medium, it adjusts the polarity of the solution, thereby effectively reducing the concentration of silicate ions (SiO3). 2-The hydrolysis and polycondensation rate of the silicate is controlled, and the nucleation and growth process is more controllable, which is the premise of forming monodisperse particles. Second, ethanol can be adsorbed on the surface of the newly formed silica particles, playing a steric hindrance effect to prevent excessive aggregation of particles. If the ratio of ethanol and water is too high (too much ethanol), the reaction rate is too slow, and the production efficiency is low. If the ratio of ethanol and water is too low (too much water), the reaction is too fast, which easily leads to explosive nucleation and particle agglomeration, and it is difficult to control monodispersity.

[0042] In the embodiment, the ratio of the sodium silicate solution to the ethanol dispersion is a volume ratio, and the volume ratio is 1:3-1:6, for example, 1:3, 1.4, and 1.59, etc. The concentration of sodium silicate in the mixed solution I is 0.2-0.4 mol / L, for example, 0.21 mol / L, 0.25 mol / L, and 0.39 mol / L, etc. This concentration range is the key to balance the nucleation density and the controllability of growth. If the concentration is too low, the number of crystal nuclei formed in a unit volume is too small, the size of the final particles grown subsequently will be large and the number will be small, and at the same time, it may lead to non-concentrated nucleation process, resulting in a wide particle size distribution (PDI). If the concentration is too high, the number of crystal nuclei formed instantaneously is too large and too fast, and the monomer concentration in the system decreases rapidly, which easily leads to the collision and aggregation of the primary particles to form irregular non-spherical agglomerates in order to reduce the surface energy, seriously degrading the sphericity and monodispersity.

[0043] In the embodiment, the ammonia solution is concentrated ammonia water with an NH3 content of 25%-28%, and the volume ratio of the addition amount of the ammonia solution to the mixed solution I is 1:20-1:30, for example, 1:21, 1:25, and 1:29, etc. Ammonia water acts as a catalyst, and its main function is to provide and maintain the alkalinity (OH - ) required by the reaction system. Under alkaline conditions, the hydrolysis and polycondensation reaction of silicate ions can proceed at an appropriate rate. The amount of ammonia water directly determines the initial pH value, thereby controlling the nucleation rate. If the amount is too small, the catalytic effect is insufficient, and the reaction is slow or even ineffective nucleation. If the amount is too large, the alkalinity of the system is too strong, which may lead to a too fast polycondensation reaction rate, and also easily cause non-uniform nucleation and agglomeration.

[0044] In the embodiment, the uniform stirring is carried out in an acid and alkali resistant reaction kettle with stirring and heating devices, the stirring speed is 100-500 r / min, and the stirring time is 20-60 min. Stable stirring ensures that the materials are fully mixed to avoid local concentration unevenness.

[0045] S2, heating and stirring the mixed solution II, adding an acid solution after reaching the set temperature, and obtaining a suspension A by reaction.

[0046] In the embodiment, the stirring speed of the heating and stirring is 100-500 r / min, such as 101 r / min, 300 r / min and 499 r / min, etc. The stirring aims to ensure the uniformity of the reaction system, avoid local high concentration or temperature gradient, too slow speed and uneven mixing, and too fast speed and introduction of too much shear force to adversely affect the fragile particle structure formed in the early stage.

[0047] In the embodiment, the set temperature is 30-60°C, such as 31°C, 40°C and 59°C, etc. The temperature is a key factor affecting the reaction rate. Too low temperature, slow reaction kinetics, time-consuming process; too high temperature, too fast reaction rate, not conducive to controllable nucleation and growth, easy to lead to wide particle size distribution.

[0048] In the embodiment, the adding of the acid solution refers to spraying the acid solution into the mixed solution II through a solution pressure pump during stirring. Compared with traditional dropwise addition, spraying can disperse the acid solution into countless micron-sized droplets instantaneously, maximize the surface area of the acid solution in contact with the alkaline sodium silicate solution, and thus realize instantaneous and uniform mixing. This can effectively avoid the pH gradient caused by local over-acidification, prevent explosive nucleation and gelation phenomenon, and is a core means to obtain a narrow distribution (PDI < 0.1) seed. The feeding speed needs to be matched, too fast still may lead to uneven mixing in local, too slow will prolong the production cycle.

[0049] In the embodiment, the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, citric acid and ascorbic acid solution, and H + The concentration is 0.5-3 mol / L, such as 0.55 mol / L, 2.0 mol / L and 2.9 mol / L, etc. Too high concentration may lead to too fast reaction rate, make the spherical silica agglomerate due to fast nucleation, and thus reduce the dispersibility; at the same time, it is not conducive to the formation of spherical particles, leading to a decrease in sphericity.

[0050] In the embodiment, the speed of adding the acid solution is 500-2000 mL / (min·m 2 ), such as 501 mL / (min·m 2 ), 1000 mL / (min·m 2 ) and 1999 mL / (min·m 2 ) etc. The speed needs to be matched with the stirring effect and the size of the reaction kettle to ensure that the acid solution can be quickly dispersed. Too fast speed will lead to a sharp drop in pH, causing uneven nucleation; too slow speed will make the whole process uneconomical.

[0051] In the present embodiment, the heating and stirring time is 2-4h, where the time refers to the time from the beginning to the end of the reaction; the pH value of the suspension A is 10-10.5, the particle size of the suspension A is 0.1-0.2μm, and the particle size distribution PDI is less than 0.1.

[0052] In the present embodiment, the pH value of 10-10.5 is the most suitable window for the nucleation and spherical growth of silica. In this alkaline environment, the particle surface is negatively charged, and good dispersion stability is maintained by electrostatic repulsion. The process of holding and stirring after stopping the acid addition is called "maturation", in which the newly born, imperfect small particles will be transformed into more stable and regular spherical structures through the "dissolution-redeposition" mechanism (Ostwald maturation), and the particle size distribution is further homogenized. Finally, a high-quality seed suspension A with a particle size of 100-200nm and PDI<0.1 is obtained.

[0053] S3, while the suspension A is kept in a state of heating and stirring, sodium silicate solution and acid solution are injected simultaneously to react, and the pH value is kept constant during the reaction process, and a suspension B is obtained after the reaction is completed.

[0054] In the present embodiment, the simultaneous injection of sodium silicate solution and acid solution is carried out by using a double feeding system, which includes two independent solution pressure pumps and corresponding feeding spray ports. The two feeding spray ports are symmetrically distributed on the inner side wall of the reactor, and the feeding direction forms an angle of 30°-60° with the rotation direction of the fluid generated by stirring in the reactor. The purpose of this design is to realize the instantaneous, equal and uniform mixing of the reactants (sodium silicate and acid). The symmetrical feeding and the specific angle design can make the two materials be quickly taken away and mixed by the high-speed rotating fluid as soon as they enter the reactor, so that they have reacted to form active silicic acid monomers in the solution before reaching the seed surface. This ensures the extreme uniformity of the monomer concentration field in the whole system, which is the equipment basis for avoiding local high concentration to induce secondary nucleation and ensuring the synchronous and uniform growth of all seeds.

[0055] In the present embodiment, the suspension A and the suspension B are both white suspensions.

[0056] In the present embodiment, the simultaneous injection of sodium silicate solution and acid solution is carried out by using a double feeding system, which includes two independent solution pressure pumps and corresponding feeding spray ports. The two feeding spray ports are symmetrically distributed on the inner side wall of the reactor, and the feeding direction forms an angle of 30°-60° with the rotation direction of the fluid generated by stirring in the reactor. The purpose of this design is to realize the instantaneous, equal and uniform mixing of the reactants (sodium silicate and acid). The symmetrical feeding and the specific angle design can make the two materials be quickly taken away and mixed by the high-speed rotating fluid as soon as they enter the reactor, so that they have reacted to form active silicic acid monomers in the solution before reaching the seed surface. This ensures the extreme uniformity of the monomer concentration field in the whole system, which is the equipment basis for avoiding local high concentration to induce secondary nucleation and ensuring the synchronous and uniform growth of all seeds. + The concentration of the acid solution is 0.5-2mol / L; the feeding molar ratio of the sodium silicate solution and the acid solution when they are injected simultaneously is 1:1.8-1:2.2, for example, 1:1.9, 1:2 and 1:2.1, etc. The feeding molar ratio here refers to that 1 mole of sodium silicate is fed with H+ in an amount.

[0057] In the present embodiment, the feeding speed ratio of the sodium silicate solution to the acid solution is 1:1.2~1:2.5, such as 1:1.2, 1:2.3 and 1:2.4, etc.; the injection speed of the sodium silicate solution is 300~1500 mL / (min m²), such as 301 mL / (min m²), 850 mL / (min m²) and 1499 mL / (min m²), etc.

[0058] Quantitative control of particle size: the total amount of sodium silicate added in the growth stage (V add ) is accurately calculated by formula (1): (1) Wherein, V add is the amount of sodium silicate solution added, in L; R target is the particle size of the prepared product (i.e. the prepared particle size controllable spherical silica micro powder), in m; R seed is the particle size of the particles in the suspension A, in m; ρ is the density of silica, in kg / m 3 ; M SiO2 is the molar mass of silica, with a value of 0.06008 kg / mol; N A is the Avogadro constant, with a value of 6.022·10 23 mol -1 ; C is the sodium silicate concentration, in mol / L.

[0059] The formula is derived from a large number of experimental results, based on a core assumption: under the premise of completely inhibiting secondary nucleation, all newly added SiO2 is used for the volume growth of seed particles, and the growth is isotropic. By associating the target particle size with the required amount of substance of SiO2 through the formula of the volume of a sphere, the predictable and calculable precise synthesis of particle size is realized, and the traditional experience and trial mode is abandoned.

[0060] In the present embodiment, the maintaining the heating and stirring state is maintaining the heating temperature and stirring speed in step S2, i.e. maintaining the temperature of the reaction kettle at 30-60°C, such as 31°C, 40°C and 59°C, etc., and the maintaining the stirring state is controlling the stirring speed of the reaction kettle at 100-500 r / min, such as 100 r / min, 300 r / min and 500 r / min, etc. The reaction time is 4-8 h. The maintaining the pH constant is maintaining the pH value of the mixed solution after injecting the sodium silicate solution and the acid solution by using the double feeding system, and the pH value stable means controlling the pH value to be 10.3 (fluctuation range <±0.2); this is the kinetic control strategy of "only growth, no nucleation". The higher constant pH value makes the condensation rate of silicic acid relatively slow. And the slow feeding speed ensures that the instantaneous concentration of active silicic acid monomer in the system is always lower than the critical concentration of homogeneous nucleation. Therefore, the newly generated monomer has no chance to form new nucleus, but only diffuses to the surface of the existing seed with a large specific surface area for deposition. The constant pH and temperature are the premise of maintaining the stable growth rate, and the severe fluctuation will lead to uneven growth layer, affecting the monodispersity and sphericity of the final product.

[0061] S4, aging treatment is performed on the suspension B to obtain a suspension C.

[0062] In the present embodiment, the aging treatment is a standing and aging process of the suspension B, and the temperature of the aging treatment is 25-60°C, such as 26°C, 30°C and 59°C, etc. In this stage, the external mechanical disturbance is stopped, and the particle system spontaneously transforms to a more stable thermodynamic state; it helps to further condense and strengthen the internal structure of the particle (improve the mechanical strength), and through the slight Ostwald ripening effect, the surface defects are repaired, the sphericity is better, and the particle size distribution is more concentrated. The aging temperature that is too high will significantly accelerate the Ostwald ripening process of the particle, leading to a significantly wider particle size distribution; at the same time, the condensation reaction of the particle surface silanol (Si-OH) is intensified at high temperature, which easily leads to irreversible chemical sintering or hard agglomeration between particles through siloxane bond (Si-O-Si), seriously damaging the dispersibility.

[0063] In the present embodiment, the aging time is 4h~24h, such as 5h, 12h and 23h, etc. Too short reaction time will result in insufficient internal condensation reaction, and the particle structure fails to reach a thermodynamic stable state, which is manifested as loose internal structure, too high specific surface area, and too many and active surface silicon hydroxyl groups. Such unstable particles are extremely prone to deformation, collapse or hard agglomeration due to dehydration shrinkage, capillary force or surface hydroxyl condensation in subsequent centrifugation, washing and drying processes, resulting in poor sphericity, poor dispersibility and possibly wide particle size distribution of the final product. Too long reaction time not only greatly reduces production efficiency and increases cost, but also, with excessive prolongation of the aging time, Ostwald ripening effect continues to occur, leading to gradual disappearance of small particles and continuous slow growth of large particles, which also results in wide particle size distribution.

[0064] S5, dehydrating, rinsing and drying the suspension C to obtain the spherical silica micro-powder A with controllable particle size.

[0065] In the present embodiment, the dehydration is performed by centrifugation, pressure filtration or suction filtration to increase the solid content to a wet cake with a water content of 30%~60%. Preliminary dehydration is to greatly reduce the amount of subsequent washing solvent and improve production efficiency. The rinsing uses 50%~80% ethanol solution to wash the wet cake for 2~5 times. The primary purpose of washing is to remove impurities such as sodium salt (e.g. NaCl) adsorbed on the surface of the particles and entrained in the filter cake, so that the content of sodium salt in the residual solution after rinsing is less than 0.05~0.1mmol / g. These impurities will seriously affect the conductivity, purity and application performance (such as electrical insulation in electronic packaging) of the final product. Using ethanol-water mixture instead of pure water for washing is to replace the water molecules on the surface of the particles and in the pores by using the dehydration effect of ethanol, which can effectively reduce the hard agglomeration of particles caused by the surface tension of water in the final drying process. Drying: vacuum drying, hot air drying or freeze drying can be used. Drying is the last step to remove the solvent and obtain the powder product, and is also a key step that is prone to cause hard agglomeration. Vacuum / hot air drying: low cost, suitable for conventional applications. The heating rate needs to be controlled to avoid rapid solvent vaporization and damage to the particle structure. Freeze drying: the preferred method to obtain the best dispersibility. The principle is to completely freeze the wet material at low temperature, and then sublimate the ice directly under vacuum. This process completely avoids the surface tension of gas-liquid interface, thereby maximizing the maintenance of the original dispersion state of the particles in the solution and effectively preventing the formation of hard agglomeration, which is crucial for applications requiring extremely high dispersibility.

[0066] In the embodiment, the drying method comprises one of vacuum drying, hot air drying or freeze drying; the vacuum drying is performed at a vacuum degree of 0.08-0.1 MPa, a temperature of 80-120°C and a time of 6-10 h; the hot air drying is performed at a temperature of 100-150°C, an air speed of 0.5-1.5 m / s and a time of 4-8 h; and the freeze drying is performed at a temperature of -50°C to -30°C and a time of 12-48 h.

[0067] In the embodiment, the preparation method further comprises densification treatment of the particle-size-controllable spherical silica powder A obtained in step S5 to obtain a particle-size-controllable spherical silica powder B.

[0068] In the embodiment, the densification treatment is high-temperature treatment of the particle-size-controllable spherical silica powder A by using a fluidized bed calcination system; the fluidized bed calcination system comprises a fluidized gas supply unit, a gas preheating unit, a fluidized bed reactor and a gas-solid separation unit; the fluidized gas is one of air or nitrogen, and under an air or oxygen atmosphere, high temperature can effectively decompose and burn the organic matter and residual hydroxyl groups remaining on the surface of the particle-size-controllable spherical silica powder A; under an inert atmosphere such as nitrogen, the main function is to remove adsorbed water and promote condensation and rearrangement of the silicon-oxygen network structure inside the particles. The gas speed of the fluidized gas is 0.1-0.5 m / s; the temperature of the densification treatment is 500-800°C, and the time is 1-4 h. The principle of using a fluidized bed is to use the preheated gas flow to make the particle-size-controllable spherical silica powder A in the reactor in a fluidized state to ensure that each particle is uniformly surrounded by high-temperature gas and efficient gas-solid heat transfer is achieved, thereby avoiding sintering and caking caused by local overheating in traditional static calcination, and maximizing the maintenance of the original spherical shape and monodispersity of the particles.

[0069] Example 2 The example embodiment provides a particle-size-controllable spherical silica powder, which can be prepared by the preparation method of the particle-size-controllable spherical silica powder described in example embodiment 1, and comprises the particle-size-controllable spherical silica powder A and the particle-size-controllable spherical silica powder B.

[0070] In the embodiment, the particle-size-controllable range of the particle-size-controllable spherical silica powder A is 0.2-3 μm, the monodispersity is excellent with PDI < 0.1, the phase is amorphous, the microscopic morphology is dispersed spherical, the whiteness is > 95%, the sphericity is > 0.95, and the spheroidization rate is > 98%.

[0071] In the present embodiment, the particle size controllable spherical silica powder B has a wide particle size controllable range of 0.2-3 μm, excellent monodispersity of PDI < 0.1, amorphous phase, dispersed spherical microscopic morphology, whiteness > 95%, sphericity > 0.95, spheroidization rate > 98%, water content < 0.05%, and tap density of 0.4-0.7 g / cm 3

[0072] Example 3 The present example provides an application of a particle size controllable spherical silica powder, which includes the particle size controllable spherical silica powder A prepared in Example 1 or the particle size controllable spherical silica powder B described in Example 2.

[0073] In the present embodiment, the particle size controllable spherical silica powder A is suitable for general fields with relatively low requirements for hardness and thermal stability: when the particle size is 0.2-1 μm, it is suitable for use as a catalyst carrier, a drug carrier, and a high-efficiency adsorbent; and when the particle size is 1-3 μm, it is suitable for use as a light scattering agent for high-end cosmetics, a paint matting agent, and a lightweight filler for high polymer materials.

[0074] In the present embodiment, the particle size controllable spherical silica powder B is suitable for high-end and precision fields: when the particle size is 0.2-1 μm, it is suitable for use as a high-density filler for epoxy plastic encapsulation for electronic packaging, a key abrasive for semiconductor wafer chemical mechanical polishing slurry, and a thermal conductivity enhancing filler for thermal conductive silicone grease; and when the particle size is 1-3 μm, it is suitable for use as a chromatographic column filler for high-performance liquid chromatography, a scratch-free polishing material for precision ceramic or metal devices, and a functional skin feel regulator for high-end cosmetics.

[0075] In order to better understand the above-mentioned example embodiments of the present application, the following further describes them in combination with specific examples.

[0076] Example 1 The present example aims to prepare a monodisperse spherical silica powder with a particle size of about 200 nm, which is mainly used as a benchmark seed for high-end cosmetic skin feel regulators or electronic packaging fillers, and the preparation method includes the following steps: Seed preparation: 4.5 mL of concentrated ammonia water was added to a 0.22 mol / L sodium silicate solution prepared in a solvent of anhydrous ethanol and water in a volume ratio of 1:1.6, and the ammonia water was added in a volume ratio of 1:25 to the mixed solution I. The mixed solution II was heated to 31°C in a water bath, and a 2.0 mol / L hydrochloric acid solution was pumped at a rate of 600 mL / (min·m 2 ​) of 1000 mL / (min.m2) to the reaction system, and the reaction was continued for 6 hours. The pH value of the system was 10.2. The obtained suspension A had a seed particle size of 180 nm and a PDI of 0.07.

[0077] Seed growth: The target particle size of this example was 200 nm, which was close to the seed particle size, so no additional growth step was needed. The seed suspension A was directly subjected to post-treatment.

[0078] Post-treatment: The suspension A was placed in a constant-temperature oven at 35°C for aging for 5 hours, and then centrifuged at 7000 r / min for 6 minutes by using a centrifugal dewatering machine. The suspension was washed 4 times with 60% ethanol solution until the residual solution had a sodium salt content of 0.07 mmol / g. Vacuum drying was performed under the following conditions: vacuum degree 0.085 MPa, drying temperature 100°C, and drying time 7 hours, to obtain spherical silica powder A. The spherical silica powder A was calcined in a fluidized bed at 501°C for 3.9 hours under the following conditions: fluidizing gas nitrogen, and fluidizing gas velocity 0.15 m / s, to obtain spherical silica powder B.

[0079] The final product obtained in Example 1 had an average particle size of 198 nm, a PDI of 0.08, a whiteness of 96%, a sphericity of 0.98, a spheroidization rate of 98.5%, a tap density of 0.4 g / cm3, and a loss on ignition at 950°C of 0.25%. The morphology of the product is shown in the SEM image of the sample SDP-1 in FIG. 1. The product had good dispersibility and high sphericity, and no obvious adhesion or agglomeration between the spheres was observed. The particle size distribution of the product is shown in the particle size distribution graph of the sample in FIG. 2. The distribution was narrow and unimodal, indicating that the spherical silica powder prepared by the method had excellent monodispersity. 3 Figure 2 The morphology of the product obtained in Example 1 is shown in the SEM image of the sample SDP-1 in FIG. 1. The product had good dispersibility and high sphericity, and no obvious adhesion or agglomeration between the spheres was observed. Figure 5 The particle size distribution of the product obtained in Example 1 is shown in the particle size distribution graph of the sample in FIG. 2. The distribution was narrow and unimodal, indicating that the spherical silica powder prepared by the method had excellent monodispersity.

[0080] Example 2 This example shows the growth of seeds from about 200 nm to 1.0 μm. The product obtained can be used for CMP polishing or high-end electronic packaging. The preparation method comprises the following steps: Seed preparation: 8 mL of concentrated ammonia water was added to a 0.25 mol / L sodium silicate solution prepared in anhydrous ethanol and water with a volume ratio of 1:2 as the solvent. The volume ratio of the added ammonia water to the mixed solution I was 1:22. The mixed solution II was heated to 50°C in a water bath, and a 1.5 mol / L hydrochloric acid solution was sprayed into the reaction system at a rate of 1000 mL / (min.m2) by using a solution pressure pump. When the pH value of the system reached 10.2, the addition of acid was stopped. The reaction was continued for 6 hours under the condition of a temperature of 50°C and stirring at 300 r / min. The obtained suspension A had a seed particle size of 180 nm and a PDI of 0.07. 2

[0081] ​​Seed growth: keep the temperature of suspension A at 50℃, stirring speed at 500r / min. Add 650mL of 0.4mol / L sodium silicate solution (calculated according to formula (1)) and 1.5mol / L hydrochloric acid solution. Through two independent solution pressure pumps, the feeding port is at an angle of 45° with the stirring direction, A pump delivers 0.4mol / L sodium silicate solution at a flow rate of 800mL / (min·m2), B pump delivers 1.5mol / L hydrochloric acid solution, the molar ratio of H + :SiO3 2- =2.0:1. Keep the pH value of the reaction system at 10.2±0.15, and the reaction time is 6 hours.

[0082] Post-processing: keep the suspension B in a constant temperature oven at 40℃ for 12 hours, and use suction filtration to remove water. The water content of the product is 45%. Wash with 70% ethanol solution for 3 times until the residual solution contains 0.06mmol / g of sodium salt. Use hot air drying, the conditions are: hot air temperature 120℃, air speed 1.0m / s, drying time 6 hours, to obtain spherical silica powder A. Calcine the spherical silica powder A in a fluidized bed at 600℃ for 2h, with air as the fluidizing gas and the fluidizing gas speed at 0.3m / s, to obtain spherical silica powder B.

[0083] The average particle size of the final product obtained in Example 2 is 1.18μm, the PDI is 0.07, the whiteness is 96.2%, the sphericity is 0.97, the spheroidization rate is 99%, the tap density is 0.5g / cm 3 , and the loss on ignition at 950℃ is 0.3%. The morphology is shown in the SEM image of sample SDP-2 in Figure 3 , which has good dispersibility and high sphericity, and no obvious adhesion and agglomeration between the spheres. The particle size distribution is shown in the particle size distribution graph of the sample in Figure 6 , which shows a narrow distribution single peak, indicating that the spherical silica powder prepared by the method has excellent monodispersity.

[0084] Example 3 This example shows the preparation of large particle size particles in the order of microns, which is suitable for high-grade paint matting agent or 3D printing material, and the preparation method comprises: Seed preparation: add 10mL of concentrated ammonia water to a 0.39mol / L sodium silicate solution prepared with anhydrous ethanol and water in a volume ratio of 1:2.4 as the solvent, and the volume ratio of ammonia water to mixed solution I is 1:20. Heat the mixed solution II to 59℃ in a water bath, and add 3mol / L hydrochloric acid solution through a solution pressure pump at a flow rate of 1999mL / (min·m 2The acid was sprayed into the reaction system at a rate of 160 nm. When the pH of the system reached 10.5, the acid addition was stopped, and the reaction was continued for 6 hours while maintaining the temperature at 60 °C and stirring at 500 r / min. Suspension A was obtained, with a seed particle size of 160 nm and a PDI of 0.08.

[0085] Seed growth: Maintain the temperature of suspension A at 60℃ and the stirring speed at 600 r / min. 2300 mL of 0.5 mol / L sodium silicate solution (calculated according to formula (1)) and 25 mol / L hydrochloric acid solution were added. Two independent solution pressure pumps were used, with the inlet at a 45° angle to the stirring direction. Pump A delivered 0.4 mol / L sodium silicate solution at a flow rate of 2000 mL / (min·m²), and pump B delivered 2 mol / L hydrochloric acid solution. The feed molar ratio H... + SiO3 2- =2.2:1. The pH of the reaction system was kept stable at 10.5±0.15, and the reaction time was 8 hours.

[0086] Post-processing: Suspension A was aged in a 50℃ constant temperature oven for 22 hours, then dehydrated by pressure filtration, with a product water content of 50%. It was washed five times with 75% ethanol solution until the sodium salt content in the residual solution was 0.05 mmol / g. Spherical silica powder A was obtained by freeze-drying at -40℃ for 36 hours. Spherical silica powder A was then calcined at 799℃ for 1.1 hours in a fluidized bed with nitrogen as the fluidizing gas and a fluidizing gas velocity of 0.49 m / s to obtain spherical silica powder B.

[0087] The final product obtained in Example 3 had an average particle size of 2.75 μm, a PDI of 0.06, a whiteness of 97.5%, a sphericity of 0.97, a sphericity of 99%, and a tap density of 0.7 g / cm³. 3 The loss on ignition at 950℃ is 0.15%. Its morphology is as follows: Figure 4 The SEM image of the medium-sized sample SDP-D3 shows good dispersibility and high sphericity, with no obvious adhesion or agglomeration between the spheres. The particle size distribution is as follows. Figure 7 The particle size distribution diagram of the sample shows that the distribution is a narrow single peak, indicating that the spherical silica micropowder prepared by this method has excellent monodispersity.

[0088] Comparative Example 1 The preparation method described in this comparative example is as follows: Seed preparation: Prepare a 0.25 mol / L sodium silicate solution by mixing anhydrous ethanol and water in a 1:2 volume ratio. Add 8 mL of concentrated ammonia solution to the solution, with the ammonia addition volume ratio to mixed solution I being 1:22. Heat mixed solution II to 50°C in a water bath. Then, use a solution pressure pump to dispense 1.5 mol / L hydrochloric acid solution at a rate of 1000 mL / (min·m⁻²).2 ) into the reaction system, and the reaction was stopped when the pH value of the system reached 10.2. The temperature was maintained at 50°C and the stirring speed was maintained at 500 r / min, and the reaction was continued for 6 hours. A suspension A was obtained, in which the seed particle size was 180 nm and the PDI was 0.07.

[0089] Seed growth: A conventional one-time titration method was used: all the sodium silicate solution calculated in Example 2 was added into the reaction system containing seeds at one time, and then hydrochloric acid was slowly added until the pH was 10.2.

[0090] Post-processing: The suspension B was placed in a constant temperature oven at 40°C for aging for 12 hours, and then dewatering was performed by suction filtration, and the water content of the product was 45%. The product was washed with 70% ethanol solution for 3 times until the sodium salt content in the residual solution was 0.06 mmol / g. Hot air drying was performed under the following conditions: hot air temperature 120°C, air speed 1.0 m / s, and drying time 6 hours.

[0091] The morphology of the product is shown in the SEM image of sample SDP-D in Figure 8 It was found that in the final product, in addition to the target particles of about 1.2 μm, a large number of new particles with a particle size of less than 200 nm appeared, the PDI was greater than 0.3, and the monodispersity was completely destroyed.

[0092] As can be seen from the above examples and comparative examples, the product prepared by the method of the application is almost monodisperse spherical particles, the particle size distribution is uniform, the dispersion is good, and there is no obvious adhesion and agglomeration between the spheres; the sphericity is greater than 0.95, and the spherization rate is greater than 98%; in addition, the product has a narrow distribution monomodal distribution, indicating that the spherical silica powder prepared by the method has excellent monodispersity.

[0093] In summary, the advantages of the application include at least one of the following: (1) The particle size can be controlled in a wide and accurate range: by combining the "seed growth method" with the quantitative feeding model (formula 1), the product particle size can be continuously and linearly enlarged from 200 nm to several microns. This method improves the particle size control from empirical groping to accurate calculation. Users only need to input the target particle size to determine the amount of reactants added, and the repeatability and predictability are extremely strong.

[0094] (2) The product has excellent monodispersity: with the synergistic effect of the double feeding system and constant pH control (10-10.5, fluctuation <±0.2), the secondary nucleation is fundamentally inhibited, and the growth of all particles is synchronized and uniform. The particle size distribution coefficient (PDI) of the obtained micro powder is strictly less than 0.1, which meets the stringent requirements of high-end applications for material uniformity.

[0095] (3) Excellent product morphology and physical and chemical properties: the obtained silica powder has a sphericity of more than 0.95, a spheroidization rate of more than 98%, a regular shape, an amorphous phase, a whiteness of more than 95%, and a very high purity (sodium salt residue <0.1 mmol / g), and excellent comprehensive performance.

[0096] (4) High process stability and strong scalability: the entire process flow is accurately controlled, from the spray preparation of seeds to the double-feeding control of growth, to strict washing and drying, each step aims to ensure the stability and consistency between batches. At the same time, the method uses low-cost sodium silicate as raw material, compared with the traditional silicate (such as TEOS) process, it has more industrial production potential and cost advantage.

[0097] (5) Wide application field: by accurately controlling the particle size, the products produced by the same technical platform can meet the specific needs of multiple high-tech fields, including but not limited to electronic packaging, precision polishing (CMP), high-end cosmetics, chromatographic packing, high-performance coatings and 3D printing materials, etc., realizing the efficient technical coverage of "one method, multiple products".

[0098] Although the present application has been described above with reference to the example embodiments and the accompanying drawings, it should be clear to those skilled in the art that various modifications can be made to the above embodiments without departing from the spirit and scope of the claims.

Claims

1. A method for producing a spherical silica fine powder with a controlled particle size, characterized by, The preparation method comprises: 1) mixing sodium silicate solution and ethanol dispersion solution in proportion, stirring uniformly to obtain mixed solution I, adding ammonia solution to mixed solution I and stirring uniformly to obtain mixed solution II; 2) heating and stirring mixed solution II, adding acid solution after reaching the set temperature, and reacting to obtain suspension A; 3) while injecting sodium silicate solution and acid solution to react, keeping the heating and stirring state of suspension A, and maintaining constant pH during the reaction, and obtaining suspension B after the reaction; 4) performing aging treatment on suspension B to obtain suspension C; 5) performing dehydration, washing and drying on suspension C to obtain spherical silica micro powder A with controllable particle size.

2. The method for producing a spherical silica powder with a controlled particle size according to claim 1, characterized by, In step 1), the mass percentage concentration of the sodium silicate solution is 5%-10%; the ethanol dispersion solution is a mixed solution of anhydrous ethanol and water, wherein the volume ratio of anhydrous ethanol to water is 1:1.5-1:2.5; the proportion is a volume ratio, the volume ratio is 1:3-1:6; the sodium silicate concentration in the mixed solution I is 0.2-0.4 mol / L; the ammonia solution is concentrated ammonia water with NH3 content of 25%-28%, the volume ratio of the addition amount of the ammonia solution to the mixed solution I is 1:20-1:30; the uniform stirring is performed in an acid and alkali resistant reaction kettle with stirring and heating device, the stirring speed is 100-500 r / min, and the stirring time is 20-60 min.

3. The method of producing a particle size-controlled spherical silica fine powder according to claim 1, characterized by, The stirring speed of the heating and stirring in step 2) is 100-500 r / min, and the set temperature is 30-60℃; the adding of the acid solution refers to spraying the acid solution into the mixed solution II through a solution pressure pump during stirring; the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, citric acid and ascorbic acid solution, the H + concentration of the acid solution is 0.5-3 mol / L; the adding speed of the acid solution is 500-2000 mL / (min·m 2 ); the heating and stirring time is 2-4 h; the pH value of the suspension A is 10-10.5, the particle size of the particles in the suspension A is 0.1-0.2 μm, and the particle size distribution PDI is less than 0.

1.

4. The method of producing a particle size-controlled spherical silica fine powder according to claim 1, characterized by, The simultaneous injection of sodium silicate solution and acid solution in step 3) is performed by using a double feeding system, which comprises two independent solution pressure pumps and corresponding feeding spray ports. The two feeding spray ports are symmetrically distributed on the inner wall of the reactor, and the feeding direction forms an angle of 30°-60° with the fluid rotation direction generated by stirring in the reactor. The two independent feeding spray ports are used to inject the suspension A simultaneously. In step 3), the concentration of the sodium silicate solution is 0.2-0.5 mol / L, and the acid solution comprises one or more of hydrochloric acid, sulfuric acid, nitric acid, citric acid and ascorbic acid solution. The H + concentration of the acid solution is 0.5-2 mol / L. The molar ratio of the feeding speed of the sodium silicate solution to the acid solution is 1:1.8-1:2.2, and the feeding speed ratio of the sodium silicate solution to the acid solution is 1:1.2-1:2.

5. The injection speed of the sodium silicate solution is 300-1500 mL / (min m²). The addition amount of the sodium silicate solution is calculated by formula (1): （1） wherein V add is the amount of sodium silicate solution added, in L; R target is the particle size of the product produced, in m; R seed is the particle size of the particles in the suspension A, in m; p is the density of the silicon dioxide, in kg / m 3 ; M SiO2 is the molar mass of the silicon dioxide, with a value of 0.06008 kg / mol; N A is the Avogadro constant, with a value of 6.022-10 23 mol -1 ; and C is the concentration of sodium silicate, in mol / L.

5. The method of producing a particle size-controlled spherical silica fine powder according to claim 1, characterized by, In step 3), the heating and stirring state is maintained as the heating temperature and stirring speed in step 2); the constant pH is that the pH value maintained by the double feeding system is stably controlled at 10-10.5, and the pH fluctuation range is <±0.2; the reaction time is 4-8 h.

6. The method of producing a particle size-controlled spherical silica fine powder according to claim 1, characterized by, In step 4), the aging treatment is a standing aging process of the suspension B, the temperature of the aging treatment is 25°C-60°C, and the time is 4 h-24 h.

7. The method of producing a particle size-controlled spherical silica fine powder according to claim 1, characterized by, In step 5), the dehydration is a dehydration process of the suspension C by using a dehydration machine with a washing device, the dehydration machine includes one of a filter press, a suction filter and a centrifuge, and the water content of the product after dehydration is 30%-60%; the washing is washing 2-5 times by using an ethanol solution with a concentration of 50%-80% on the basis of dehydration, so that the sodium salt content in the residual solution after washing is less than 0.05-0.1 mmol / g; the drying mode includes one of vacuum drying, hot air drying or freeze drying; the vacuum drying conditions are: vacuum degree 0.08-0.1 MPa, temperature 80-120°C, and time 6-10 h; the hot air drying conditions are: temperature 100-150°C, air speed 0.5-1.5 m / s, and time 4-8 h; the freeze drying conditions are: temperature -50°C--30°C, and time 12 h-48 h.

8. The method of producing a particle size-controlled spherical silica fine powder according to claim 1, characterized by, The preparation method further comprises performing densification treatment on the spherical silica micro powder A with controllable particle size obtained in step 5) to obtain spherical silica micro powder B with controllable particle size. The densification treatment is high-temperature treatment of the particle-size-controllable spherical silica micro powder A by using a fluidized bed calcination system; the fluidized bed calcination system comprises a fluidized gas supply unit, a gas preheating unit, a fluidized bed reactor and a gas-solid separation unit; the fluidized gas is one of air or nitrogen; the gas velocity of the fluidized gas is 0.1-0.5 m / s; the temperature of the densification treatment is 500-800℃, and the time is 1-4 h.

9. A spherical silica fine powder with a controllable particle size, characterized by The particle-size-controllable spherical silica micro powder is prepared by the preparation method of the particle-size-controllable spherical silica micro powder according to any one of claims 1-8, and the particle-size-controllable spherical silica micro powder comprises the particle-size-controllable spherical silica micro powder A and the particle-size-controllable spherical silica micro powder B; The particle-size-controllable range of the particle-size-controllable spherical silica micro powder A is 0.2-3 μm, the monodispersity is excellent with PDI < 0.1, the phase is amorphous, the microscopic morphology is dispersed spherical, the whiteness is > 95%, the sphericity is > 0.95, and the spheroidization rate is > 98%; The particle size controllable spherical silica micro powder B has a wide controllable particle size range of 0.2-3 μm, excellent monodispersity PDI < 0.1, an amorphous phase, a dispersed spherical microscopic morphology, whiteness > 95%, sphericity > 0.95, spheroidization rate > 98%, water content lower than 0.05%, and tap density of 0.4-0.7 g / cm 3 Thermogravimetric analysis shows that the weight loss is less than 0.5% at 950℃.

10. The use of the spherical silica fine powder of claim 9, wherein the spherical silica fine powder is used as a filler for a rubber composition. The particle-size-controllable spherical silica micro powder A is suitable for general fields with relatively low requirements on hardness and thermal stability: when the particle size is 0.2-1 μm, it is suitable for being used as a catalyst carrier, a drug carrier and a high-efficiency adsorbent; when the particle size is 1-3 μm, it is suitable for being used as a light scattering agent for high-end cosmetics, a matte agent for coatings and a light filler for high polymer materials; The particle-size-controllable spherical silica micro powder B is suitable for high-end and precision fields: when the particle size is 0.2-1 μm, it is suitable for being used as a high-density filler for epoxy plastic encapsulating material for electronic packaging, a key abrasive for semiconductor wafer chemical mechanical polishing slurry and a heat-conducting enhancement filler for heat-conducting silicone grease; when the particle size is 1-3 μm, it is suitable for being used as a column filler for high-performance liquid chromatography, a scratch-free polishing material for precision ceramic or metal devices, and a functional skin feel regulator for high-end cosmetics.

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