Micro-silicon powder, preparation method and application thereof

Abstract

The present application relates to the field of inorganic non-metallic materials, and more particularly to a micro-silicon powder, a preparation method and applications thereof. The preparation method comprises: heat treatment, screening, water washing and sedimentation, and / or silane coupling agent modification of the industrial raw micro-silicon powder. The present application innovatively combines precise temperature control heat treatment, green physical purification and targeted chemical modification, and simultaneously realizes deep impurity removal (carbon and soluble alkali metals) and surface hydrophobic modification on the premise of preserving the key spherical morphology and pozzolanic activity of the micro-silicon powder.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials, and more specifically, to a microsilica powder, its preparation method, and its application. Background Technology

[0002] Microsilica, also known as silica fume, is a major byproduct of industrial silicon or ferrosilicon alloy smelting in electric arc furnaces. Under a high-temperature reducing atmosphere, the SiO and CO gases generated by the reaction of silica with carbonaceous reducing agents escape from the furnace. After rapid oxidation and condensation, they form extremely fine (typically 0.1-0.3 μm) spherical amorphous (non-crystalline) silica particles with a large specific surface area (15-30 m² / g), which are then collected by a dust removal device. As a major industrial solid waste, the main chemical component of microsilica is silica (SiO2 content is usually above 85%), while also containing small amounts of metal oxides such as potassium, sodium, calcium, and iron, as well as free carbon impurities. Due to its unique ultrafine particle morphology, high pozzolanic activity, and high refractoriness, microsilica has become a key component of modern high-performance unshaped refractory materials, especially castables. In refractory castables, the core mechanisms of action of microsilica mainly include: ultrafine microsilica particles possess excellent physical filling effects, effectively filling the pores between aggregates and fine powders, optimizing particle size distribution, significantly reducing water consumption, and increasing the density and bulk density of the castable; furthermore, the pozzolanic reactivity of microsilica promotes enhanced bonding of the material. At room temperature, the active SiO2 on the surface of microsilica reacts with Ca(OH)2 produced by the hydration of binders (such as calcium aluminate cement) to generate hydrated calcium silicate (CSH) gel. This gel can encapsulate and connect particles, significantly improving the demolding strength and room temperature strength of the castable. At high temperatures, microsilica promotes the formation of high-temperature phases such as mullite, strengthening the matrix structure. In addition, the "ball effect" of microsilica can improve the rheological properties of the mixture, enabling it to maintain good fluidity and thixotropy even at low water content, facilitating construction and casting. Therefore, microsilica powder is widely used in various mid-to-high-end refractory castables such as aluminum-silicon, corundum, silicon carbide-containing, and magnesium-based refractory castables. It is an indispensable micro powder material for the preparation of low-cement castables (CaO content 1.0-2.5%) and ultra-low-cement castables (CaO content 0.2-1.0%).

[0003] Although the application of microsilica is widespread, its inherent characteristics as an industrial byproduct bring a series of technical challenges to high-performance refractory castables. Existing solutions mostly focus on direct use in formulations or simple pretreatment. The current technical approach of directly applying microsilica mainly faces the following bottlenecks: 1) The chemical composition (such as SiO2 purity and alkali metal impurity content), physical properties (such as particle size distribution and specific surface area), and residual carbon content of microsilica are affected by the source of raw materials, smelting processes, and dust collection methods, leading to fluctuations in the workability, mechanical strength, and high-temperature performance of the final castable product, making it difficult to meet the requirements of high-end applications. 2) The huge specific surface area of ​​microsilica significantly increases the water demand of the mixture, easily leading to moisture evaporation during baking and sintering, leaving more pores and increasing sintering shrinkage, which adversely affects the intermediate-temperature strength and final volume stability of the castable. 3) Low-melting-point alkali metal impurities such as K₂O and Na₂O in microsilica powder can lower the high-temperature liquidus temperature of the material, worsening its high-temperature creep resistance and corrosion resistance. Furthermore, the presence of free carbon may affect certain castable systems that are sensitive to oxygen partial pressure or require specific colors. 4) Unmodified microsilica powder is prone to forming hard agglomerates due to van der Waals forces. These agglomerates are difficult to effectively disperse and wet during castable mixing, failing to provide ultrafine filling and activation effects and instead becoming structural defects that impair the material's homogeneity and strength. Therefore, there is an urgent need to develop a highly dispersible and stable microsilica powder for use in refractory castables. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing microsilica powder, comprising: heat treatment of industrial raw microsilica powder, sieving, water washing and sedimentation, and / or modification with a silane coupling agent.

[0005] This invention utilizes a three-step integrated process of "precise temperature-controlled heat treatment → sieving, washing and sedimentation → silane coupling agent surface modification" to systematically transform unstable industrial by-product microsilica powder into high-purity, highly dispersed, and low-water-requirement high-performance refractory castable powder. The technology has significant effects and remarkable industrial applicability.

[0006] In one embodiment of the present invention, the heat treatment includes: heating to a first temperature range under a protective atmosphere, switching to an oxygen-containing atmosphere, and holding at the first temperature range; and cooling under a protective atmosphere.

[0007] This invention achieves maximum removal of harmful impurities and reduces particle sintering of microsilica powder by precisely controlling the temperature below its crystal transformation temperature; it also preserves the amorphous active structure while removing carbon.

[0008] In this embodiment, the specific oxygen content in the oxygen-containing atmosphere is not limited, as long as oxidation can be achieved. A pure oxygen atmosphere or an air atmosphere can be selected.

[0009] In one embodiment of the present invention, the first temperature range is 700℃-790℃; In one embodiment of the present invention, the heating rate is 5-10°C / min. In one embodiment of the present invention, the heat preservation time is 1-2 hours; In one embodiment of the present invention, the cooling conditions are: first, rapid cooling to below 300°C, and then natural cooling to room temperature.

[0010] In one embodiment of the present invention, the rapid cooling rate is 50-80°C / min.

[0011] In one embodiment of the present invention, the protective atmosphere is a rare gas atmosphere or a nitrogen atmosphere.

[0012] This invention creatively controls the heat treatment temperature strictly within a narrow window of 700-790℃ and employs a segmented control strategy of inert / oxidizing atmosphere. Compared to traditional high-temperature calcination (>850℃) for carbon removal, excessively high temperatures can cause the silica fume particles to sinter and crystallize, thus losing their amorphous structure and high pozzolanic activity. The temperature control technology of this invention ensures sufficient oxidation and removal of free carbon while preserving the inherent submicron spherical morphology and amorphous structure of the silica fume to the greatest extent possible, retaining its key physicochemical properties from the source and laying the foundation for the effective implementation of subsequent steps. Within this temperature range, the C content decreased from 2.1% to 0.15%, and XRD showed that the silica fume sample had an amorphous structure, while SEM images clearly showed spherical particles.

[0013] In one embodiment of the present invention, the screening, washing, and sedimentation includes: screening industrial raw silica powder or heat-treated silica powder by particle size; mixing the screened silica powder with water to obtain a uniform slurry; and subjecting the uniform slurry to sedimentation, solid-liquid separation, and drying.

[0014] This invention replaces acid washing with sieving and water washing sedimentation to treat soluble impurities and high-temperature sintered particles in microsilica powder, ensuring that the obtained samples have basically consistent particle sizes.

[0015] In one embodiment of the present invention, the particle size screening is performed on particles smaller than 45 μm.

[0016] Choosing particles smaller than 45μm can avoid particle size segregation caused by large impurities, resulting in more uniform particle size.

[0017] In one embodiment of the present invention, the solid-liquid ratio of the microsilica powder to water is (1:5)-(1:10).

[0018] When the solid-liquid ratio is greater than 1:5, the slurry is viscous, the stirring resistance is high, and the agglomerates cannot be broken up. After washing, the removal rates of alkali and carbon content will decrease. When the solid-liquid ratio is less than 1:10, some nano-sized silica powder will be lost with the washing wastewater during the washing and solid-liquid separation process, resulting in a decrease in the powder recovery rate.

[0019] In one embodiment of the present invention, the mixing conditions are: rotation speed of 200-400 rpm.

[0020] In one embodiment of the present invention, after obtaining the uniform slurry, the process further includes continuous stirring for 30-40 minutes.

[0021] In one embodiment of the present invention, the settling time is 2-4 hours.

[0022] In one embodiment of the present invention, the drying conditions are: drying at 80-105°C for 6-12 hours.

[0023] This invention innovatively adopts a purification route that combines multi-stage physical sieving with deionized water circulation washing and gravity sedimentation, replacing the common acid washing method (such as hydrofluoric acid) in the industry. It solves the defects of acid washing method, such as high toxicity, strong corrosion, environmental pollution and possible excessive erosion of powder surface. In addition, the uneven particle size and impurity distribution of the original powder will affect the dispersibility of the powder.

[0024] The sieving, washing, sedimentation, and purification method of this invention does not use hydrofluoric acid, thus avoiding fluoride pollution and the corrosive hazards of strong acids. It is safer to operate. The sieving removes large sintered particles, the washing effectively dissolves and removes soluble alkali metal impurities such as K2O and Na2O, and the sedimentation classification results in a more uniform high-purity microsilica powder with a significantly narrowed particle size distribution range (D90 / D10 < 4), improving product consistency.

[0025] In one embodiment of the present invention, the modification of the silane coupling agent includes: mixing industrial raw microsilica powder, heat-treated microsilica powder, or microsilica powder after sieving, washing and settling with a solvent, and acidifying it; adding the silane coupling agent dropwise into the acidified solution to react; and separating and drying it.

[0026] Surface modification of microsilica powder samples by silane coupling agents ensures high dispersibility and stable performance of the obtained samples.

[0027] In one embodiment of the present invention, the solid-liquid ratio of the industrial raw silica powder, the heat-treated silica powder, or the silica powder after screening, washing and settling to the solvent is 1:10-20.

[0028] When the solid-liquid ratio of silica powder to solvent is greater than 1:10, the slurry is viscous and the agglomerates cannot be broken up. The coupling agent can only coat the outer layer of the powder agglomerates, and the inner layer of powder is not grafted. After modification, the interfacial bonding force between the powder and the organic matrix is ​​greatly reduced. When the solid-liquid ratio is less than 1:20, the solvent loss rate increases.

[0029] In one embodiment of the present invention, the solvent is a mixture of ethanol and water; preferably, the volume ratio of ethanol to water is (8~10):1.

[0030] If the water content is too high (alcohol-to-water ratio less than 8:1), it can lead to silane self-polymerization and powder agglomeration; if the alcohol content is too high (alcohol-to-water ratio greater than 10:1), hydrolysis will be insufficient.

[0031] In one embodiment of the present invention, the acidification is to adjust the pH value of the solution to 4-5.

[0032] Strong acids (pH < 4) cause the hydrolysis rate to be too fast and uncontrollable, directly triggering silane self-polymerization; under alkaline conditions (pH > 7), it reacts with Si-OH on the surface of microsilica powder, causing damage to the surface structure of the powder, and the self-polymerization tendency of hydrolysis products also increases significantly under alkaline conditions.

[0033] In one embodiment of the present invention, the silane coupling agent is at least one selected from γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or γ-methacryloyloxypropyltrimethoxysilane.

[0034] In one embodiment of the present invention, the amount of the silane coupling agent added is 0.5-3.0% of the mass of the microsilica powder.

[0035] Excessive silane coupling agent (>3.0%) not only wastes raw materials but also causes a series of powder performance defects; insufficient silane coupling agent (less than 0.5%) results in insufficient silane dosage, and a large number of uncoated hydrophilic hydroxyl groups remain on the surface of the silicon micropowder, which are still prone to agglomeration after modification, and the improvement of interfacial bonding is limited.

[0036] In one embodiment of the present invention, the reaction conditions are: 50-80°C, 1-2 hours.

[0037] In one embodiment of the present invention, the drying conditions are: vacuum drying at 60-85°C.

[0038] In one embodiment of the present invention, the drying time is 7-10 hours.

[0039] In one embodiment of the present invention, the separation is performed by centrifugation, and the mixture is repeatedly washed with ethanol to remove the physically adsorbed coupling agent.

[0040] This invention innovatively selects specific silane coupling agents such as KH-570 (γ-(methacryloyloxy)propyltrimethoxysilane) to perform surface chemical grafting modification on high-purity microsilica powder in an acidic ethanol-water system. This solves the technical problems of high surface energy and strong hydrophilicity of microsilica powder, which lead to poor dispersibility, easy agglomeration, and high water demand in castables.

[0041] After hydrolysis of silane, a strong Si-O-Si covalent bond is formed with the Si-OH on the powder surface to form a stable coating. The grafted organic long chain imparts hydrophobicity to the powder, significantly reducing surface energy and thus reducing its water requirement in the castable. The resulting powder can achieve the required flowability of refractory castable under a solid-liquid ratio of 2:1 (when poured from a height of 10 cm onto a flat plate, the slurry flows and diffuses due to gravitational potential energy to form a circular area with a diameter >10 cm). At the same time, the steric hindrance effect generated by the long chain can effectively prevent particle re-agglomeration, achieving nanoscale uniform dispersion in the matrix, giving full play to the micro powder filling effect and improving dispersion performance.

[0042] On the other hand, a microsilica powder is also provided, which is prepared by any of the above methods.

[0043] On the other hand, a microsilica powder is also provided, with SiO2 content greater than 90wt%, carbon content less than or equal to 0.18wt%, activation index greater than or equal to 10%, flexural strength at 110℃×24h greater than or equal to 6.5MPa, and flexural strength at 1100℃×3h greater than or equal to 10.5MPa.

[0044] Preferably, the SiO2 content is greater than 93wt%, the carbon content is less than or equal to 0.12wt%, the activation index is greater than or equal to 20%, the flexural strength at 110℃ for 24h is greater than or equal to 6.9MPa, and the flexural strength at 1100℃ for 3h is greater than or equal to 12.5MPa.

[0045] More preferably, the carbon content is less than or equal to 0.1 wt%, the activation index is greater than or equal to 95%, the flexural strength at 110℃ for 24h is greater than or equal to 8 MPa, and the flexural strength at 1100℃ for 3h is greater than or equal to 16 MPa.

[0046] On another front, an application of microsilica powder is also provided for high-performance refractory castables.

[0047] The beneficial effects of this patent: This invention innovatively combines precise temperature-controlled heat treatment, green physical purification, and targeted chemical modification. While preserving the key spherical morphology and pozzolanic activity of the microsilica powder, it simultaneously achieves deep impurity removal (carbon and soluble alkali metals) and surface hydrophobic modification. The resulting microsilica powder product not only has high purity and good batch stability, but also directly reduces the water requirement of refractory castables by 10%-25%. Furthermore, its excellent dispersibility significantly improves the density and high-temperature performance of the castable, achieving a leap from "industrial by-product" to "high-performance customized raw material".

[0048] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, etc. Attached Figure Description

[0049] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0050] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the microsilica powder sample obtained in Example 1 of this invention.

[0051] Figure 2 This is a scanning electron microscope (SEM) image of the microsilica powder sample obtained in Example 1 of the present invention.

[0052] Figure 3 This is a particle size distribution diagram of the microsilica powder sample obtained in Example 2 of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of specific embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is also expected that ranges of 60 to 110 and 80 to 120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0056] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0057] In this application, "multiple" means two or more (including two).

[0058] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0059] Existing solutions for treating microsilica powder mostly focus on the composite design of refractory castable formulations, that is, directly incorporating undisturbed or simply processed microsilica powder as one of multiple micropowder components into the mixture. Compared with the current mainstream single-processing solutions in the industry (such as directly using undisturbed powder, separate acid washing, or high-temperature calcination), the core advantage of this invention lies in its systematic solution to multiple contradictions that existing technologies cannot address simultaneously through an integrated and synergistic process chain.

[0060] Specifically, while current technologies (such as acid washing purification or high-temperature decarbonization) can solve the purity or decarbonization problems respectively, they often introduce new drawbacks: acid washing corrodes equipment and pollutes the environment, while high-temperature treatment destroys the amorphous active structure of microsilica and leads to particle sintering. This invention innovatively combines precise temperature-controlled heat treatment, green physical purification, and targeted chemical modification. While preserving the key spherical morphology and pozzolanic activity of the microsilica, it simultaneously achieves deep impurity removal (carbon and soluble alkali metals) and surface hydrophobic modification. The resulting microsilica product not only has high purity and good batch stability, but also directly reduces the water requirement of refractory castables by 10%-25%, and significantly improves the density and high-temperature performance of the castable due to its excellent dispersibility, achieving a leap from "industrial by-product" to "high-performance customized raw material."

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the following will describe in detail a method for preparing microsilica powder for refractory castables according to this invention, in conjunction with the accompanying drawings and specific experimental data. The following examples and comparative examples are for illustrative purposes only and are not intended to limit the scope of this invention.

[0062] Example 1 Step a, Heat Treatment: Weigh 200g of undisturbed silica powder (the same as the industrial undisturbed silica powder in Comparative Example 1), spread it evenly in an alumina crucible, and place it in a box-type programmable temperature-controlled calcination furnace. First, introduce high-purity nitrogen (flow rate 0.5 L / min) for protection, and program the temperature to 750℃ at a rate of 8℃ / min. After reaching the set temperature, switch the atmosphere to dry air (flow rate 0.5 L / min) and maintain the temperature at 750℃ for 1.5 hours to allow the free carbon to be fully oxidized. After the temperature is maintained, switch back to the nitrogen atmosphere, open the furnace door to allow the sample to cool rapidly (cooling rate 60℃ / min) to below 300℃, and then allow it to cool naturally to room temperature to obtain heat-treated silica powder.

[0063] Performance characterization: The composition, phase composition and subsequent application of the heat-treated microsilica powder were tested.

[0064] Example 2 Step a is the same as in Example 1, resulting in heat-treated powder.

[0065] Step b1, sieving and washing: Pass the heat-treated powder through an 800-mesh (approximately 18 μm) standard sieve to remove any possible trace amounts of sintered agglomerates. Take 150 g of the sieved fine powder and place it in a glass container equipped with a stirrer. Add 1200 ml of deionized water at a solid-liquid ratio of 1:8. Stir continuously at 400 rpm for 40 minutes to form a homogeneous slurry.

[0066] Step b2, Sedimentation and Drying: Transfer the slurry to a 2L conical settling tank and let it stand for 3 hours. Carefully extract the upper suspended slurry and perform vacuum filtration using a Buchner funnel. Wash the filter cake three times with deionized water. Place the washed filter cake in a vacuum drying oven and dry it at 100℃ and normal pressure for 10 hours. After drying, remove it and lightly grind it to obtain high-purity microsilica powder.

[0067] 4. Performance characterization: The composition, phase composition and subsequent application of the high-purity microsilica powder were tested.

[0068] Example 3 Steps a, b1, and b2 are the same as in Example 2.

[0069] Step c1, Surface Modification: Weigh 100g of the high-purity silica powder obtained in step b2 and place it in a 500ml three-necked flask equipped with a reflux condenser and a thermostatic magnetic stirrer. Add 1500ml of a mixed solvent prepared from anhydrous ethanol and deionized water at a volume ratio of 9:1, and ultrasonically disperse for 10 minutes. Subsequently, while stirring, adjust the pH of the slurry to 4.5 with dilute acetic acid.

[0070] Step c2, coupling agent grafting: Slowly add 1.5g (1.5% of the mass of silica powder) of KH-570 silane coupling agent to the above system. Raise the water bath temperature to 60℃ and stir at a constant speed for 1.5 hours at this temperature.

[0071] Step c3, post-processing: After the reaction, the slurry was transferred to a centrifuge tube and centrifuged at 8000 rpm for 5 minutes, discarding the supernatant. The precipitate was repeatedly dispersed and centrifuged three times with anhydrous ethanol to remove the physically adsorbed coupling agent. Finally, the washed powder was placed in a vacuum drying oven and dried at 80°C for 8 hours to obtain the final product—surface-modified microsilica powder.

[0072] Performance characterization: Comprehensive tests were conducted on the composition, powder properties, and castable application performance of the surface-modified microsilica powder.

[0073] Example 4 Step: Repeat the complete process of Example 3, except that the volume ratio of anhydrous ethanol to deionized water in step c1 is changed from "V(ethanol):V(water)=9:1" to "V(ethanol):V(water)=8:1", and all other parameters (pH value, type and amount of coupling agent, reaction temperature and time, etc.) remain unchanged.

[0074] Performance characterization: The activation index and water requirement of the castable were tested on the obtained modified powder.

[0075] Example 5 Step: Repeat the complete process of Example 3, except that the silane coupling agent in step c2 is changed from "KH-570" to an equal mass (1.5g) of "KH-560 (γ-glycidoxypropyltrimethoxysilane)", and all other parameters remain unchanged.

[0076] Performance characterization: The activation index and castable strength of the obtained modified powder were tested.

[0077] Example 6 In step a, the temperature is raised to 700℃ at a rate of 5℃ / min, held for 2 hours, and rapidly cooled at a rate of 80℃ / min. In step b1, the sample is sieved through a 325-mesh screen, the solid-liquid ratio is 1:5, and the mixture is stirred for 35 minutes at a speed of 200 rpm. In step b2, the settling time is 4 hours, and the sample is dried at 105℃ and -0.09 MPa for 6 hours. In step c1, the volume ratio of ethanol to water is 8:1, the pH is adjusted to 4, and the solid-liquid ratio of silica powder to solvent is 1:10. In step c2, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane, the amount of silane coupling agent added is 0.5% of the mass of silica powder, the reaction conditions are 50℃ for 2 hours, and the drying conditions are vacuum drying at 60℃ for 10 hours. Other conditions are the same as in Example 3.

[0078] Performance characterization: The activation index and castable strength of the obtained modified powder were tested.

[0079] Example 7 In step a, the temperature is raised to 790℃ at a rate of 10℃ / min, held for 1 hour, and rapidly cooled at a rate of 80℃ / min. In step b1, the solid-liquid ratio is 1:10, and the mixture is stirred for 30 minutes at a speed of 300 rpm. In step b2, the settling time is 2 hours, and the mixture is dried at 80℃ and -0.09 MPa for 12 hours. In step c1, the volume ratio of ethanol to water is 10:1, the pH is adjusted to 5, and the solid-liquid ratio of silica powder to solvent is 1:20. In step c2, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane, the amount of silane coupling agent added is 3.0% of the mass of silica powder, the reaction conditions are 80℃ for 1 hour, and the drying conditions are vacuum drying at 85℃ for 7 hours. Other conditions are the same as in Example 3.

[0080] Performance characterization: The activation index and castable strength of the obtained modified powder were tested.

[0081] Comparative Example 1 This comparative example uses industrial-grade raw microsilica powder to simulate the most common existing technology solutions.

[0082] Raw material: Raw silica powder collected from the dust removal system of an electric arc furnace in a steel plant, without any processing.

[0083] Performance characterization: The original silica powder and its formulated castables were tested directly.

[0084] Comparative Example 2 In step a, the temperature is raised to 850°C, and the rest is the same as in Example 3.

[0085] Comparative Example 3 No oxidation is performed in step a, otherwise it is the same as in Example 3.

[0086] Effect verification and data analysis To quantitatively evaluate the effectiveness of this invention, all microsilica powder samples obtained from comparative examples and embodiments were subjected to uniform testing. The testing methods are as follows: Chemical composition: The contents of SiO2, K2O and Na2O were determined by X-ray fluorescence spectrometry; the carbon content was determined by carbon-sulfur analyzer.

[0087] Phase analysis: The crystal structure was analyzed using X-ray diffraction.

[0088] Powder properties: BET specific surface area was determined by nitrogen adsorption method; activation index was determined by the flocculation rate of powder in water.

[0089] Performance of Castables: Each sample was prepared into calcium aluminate cement-bonded corundum castable blocks according to the same formula (each sample was replaced with 5 wt% of the equivalent amount of SiO2 micro powder in the reference formula). The water requirement required to reach the standard consistency was tested, and after drying at 110℃ and heat treatment at 1100℃, the flexural strength was tested.

[0090] The test results for each embodiment and comparative example are shown in Table 1.

[0091] Table 1: Properties of microsilica powder in each example and comparative example and its effect on castable properties

[0092] As can be seen from the data in Table 1: 1. Effectiveness of Stepwise Optimization: Example 1 (heat treatment) successfully reduced the carbon content from 2.1% to 0.15%, and XRD showed that it remained amorphous, proving that "precise temperature control" preserved the amorphous active structure while removing carbon. Comparative Example 2 (850℃) exceeded the upper temperature limit, resulting in a decrease in the specific surface area of ​​the sintered silica powder, a significant decrease in the activation index, poor modification effect, and extremely limited improvement in various performance parameters. Comparative Example 3 (non-oxidized) did not completely remove carbon impurities, which had a significant impact on subsequent modification operations. Therefore, it had a high carbon content and a low activation index, and its performance was not much different from the untreated raw powder. Example 2 (water washing) further reduced the alkali metal impurity content significantly from 1.8% to 0.4%, and the purity was significantly improved.

[0093] 2. Synergistic and Superior Effects of the Complete Process: The product of Example 3 (complete modification), while maintaining high purity (low impurities) and amorphous structure, exhibits an activation index exceeding 95%, demonstrating that the surface has successfully changed from hydrophilic to hydrophobic, resulting in excellent dispersibility. This directly leads to a significant reduction in water requirement in the castable, and increases in strength after drying and medium-temperature firing by 45% and 60%, respectively, comprehensively addressing the problems pointed out in the background art.

[0094] 3. Adjustability and Inclusivity of Process Parameters: Example 4 shows that even with the alcohol-to-water ratio adjusted to 8:1, an excellent effect of 92% activation index and a 16% reduction in water requirement can still be achieved, proving the effectiveness of the solvent ratio within the range described in this invention. Example 5 shows that using epoxy-based silane KH-560 can also achieve a high activation index and significant strength improvement, proving the selectivity of silane coupling agents. Example 6, with a slightly lower temperature and higher water washing concentration, resulted in slightly weaker decarbonization and purification efficiency, thus a slightly higher carbon content and a slight decrease in purity and strength. Example 7, with a temperature close to the upper limit, achieved thorough decarbonization while retaining activity, with performance comparable to Example 3. This indicates that by adjusting the parameters within the scope of the claims, the final performance of the microsilica powder product is similar to that of Example 3 but with slight characteristic differences.

[0095] The above embodiments and test examples fully demonstrate that the present invention, through a three-step integrated process of "precise temperature-controlled heat treatment → sieving, washing and sedimentation → silane coupling agent surface modification", can systematically transform unstable industrial by-product microsilica powder into high-purity, highly dispersed, low-water-requirement high-performance refractory castable powder. The technical effect is significant, and it has outstanding creativity and industrial applicability.

[0096] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes to the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection of this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for preparing microsilica powder, characterized in that, include: Industrial raw microsilica powder is subjected to heat treatment, sieving, water washing and sedimentation and / or modification with silane coupling agents.

2. The preparation method according to claim 1, characterized in that, The heat treatment includes: heating to a first temperature range under a protective atmosphere, switching to an oxygen-containing atmosphere, and holding at the first temperature range; and cooling under a protective atmosphere.

3. The preparation method according to claim 2, characterized in that, The first temperature range is 700℃-790℃; And / or the heating conditions are 5-10℃ / min; And / or the heat preservation time is 1-2 hours; And / or the cooling conditions are: first rapidly cooling to below 300°C, then naturally cooling to room temperature; further, the rapid cooling rate is 50-80°C / min; And / or the protective atmosphere is a rare gas atmosphere or a nitrogen atmosphere.

4. The preparation method according to claim 1, characterized in that, The screening, washing, and sedimentation process includes: screening industrial raw silica powder or heat-treated silica powder by particle size; mixing the screened silica powder with water to obtain a uniform slurry; and subjecting the uniform slurry to sedimentation, solid-liquid separation, and drying.

5. The preparation method according to claim 4, characterized in that, The particle size screening is for particles smaller than 45 μm; And / or the solid-liquid ratio of the microsilica powder to water is (1:5)-(1:10); And / or the mixing conditions are: rotation speed 200-400 rpm; And / or after obtaining a uniform slurry, the process further includes continuous stirring for 30-40 minutes; And / or the settlement time is 2-4 hours; And / or the drying conditions are: drying at 80-105℃ for 6-12 hours.

6. The preparation method according to claim 1, characterized in that, The modification of the silane coupling agent includes: mixing industrial raw microsilica powder, heat-treated microsilica powder, or microsilica powder after sieving, washing, and sedimentation with a solvent, and acidifying it; adding the silane coupling agent dropwise into the acidified solution to react; and then separating and drying it.

7. The preparation method according to claim 6, characterized in that, The solid-liquid ratio of the industrial raw silica powder, heat-treated silica powder, or sieved, washed, and settled silica powder to the solvent is 1:10-20. And / or the solvent is a mixture of ethanol and water; preferably, the volume ratio of ethanol to water is (8~10):1; And / or the acidification is to adjust the pH of the solution to 4-5; And / or the silane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane or γ-methacryloyloxypropyltrimethoxysilane; And / or the amount of the silane coupling agent added is 0.5-3.0% of the mass of the microsilica powder; And / or the reaction conditions are: 50-80℃, 1-2 hours; And / or the drying conditions are: vacuum drying at 60-85°C.

8. A microsilica powder, prepared by the method described in any one of claims 1-7.

9. A microsilica powder, characterized in that, The SiO2 content is greater than 90wt%, the carbon content is less than 0.18wt%, the activation index is greater than 10%, the flexural strength at 110℃ for 24h is greater than 6.5MPa, and the flexural strength at 1100℃ for 3h is greater than 10.5MPa.

10. An application of the microsilica powder according to claim 8 or 9, characterized in that, Used in high-performance refractory castables.

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