Preparation method of nano-silica-alumina polishing composite abrasive

Abstract

The present application belongs to the technical field of inorganic nanomaterials and solid waste resource utilization, and particularly relates to a preparation method of a nano-silicon dioxide-aluminum oxide polishing composite abrasive, characterized in that aluminum elements and silicon elements in the solid waste fly ash of a coal-fired power plant are respectively converted into aluminum oxide and silicon dioxide, realizing efficient separation and utilization of aluminum-silicon double resources, including preparation of flaky aluminum oxide, preparation of silicon dioxide from desiliconized liquid, activation of aluminum oxide cores, pretreatment of silicon powder, in-situ oxidation-hydrolysis coating reaction and post-treatment.The present application has the beneficial effect that the present application uses coal-based solid waste fly ash as raw material to directionally generate high-purity flaky alpha-Al2O3 crystals in the fly ash matrix, aluminum elements (Al2O3) and silicon elements (SiO2) in the fly ash are respectively converted into aluminum oxide and nano-silicon dioxide, realizing efficient separation of silicon and aluminum elements and in-situ removal of hematite impurities, and realizing efficient separation and utilization of aluminum-silicon double resources.

Description

Technical Field

[0001] This invention belongs to the field of inorganic nanomaterials and solid waste resource utilization technology, and particularly relates to a method for preparing a composite abrasive for polishing nano-silica-alumina. Background Technology

[0002] Chemical mechanical polishing (CMP) is a key process for achieving globally planar surfaces in semiconductor manufacturing. The polishing slurry is the core of CMP technology, and the performance of the abrasive particles directly determines the polishing effect. Alumina (Al2O3) abrasives have high hardness and strong cutting force, but they easily cause scratches on the wafer surface; silicon dioxide (SiO2) abrasives have lower hardness and a smoother surface, achieving excellent surface quality, but their material removal rate (MRR) is lower.

[0003] Currently, there are techniques that use a simple physical mixture of alumina and silica, but the two behave independently during polishing, failing to synergistically enhance their effects, and uneven hardness can still lead to scratches. Research has also attempted to prepare composite abrasives, but these often suffer from uneven coating, discontinuous shell layers, and weak core-shell bonding, making them prone to peeling during polishing and unable to stably leverage the advantages of the core-shell structure. Existing technologies mostly use silicates, silica sols, or silanes as silicon sources, which are either costly or involve complex processes.

[0004] Chinese invention patent application number 202210363963.2 discloses a polishing composition comprising: composite particles, including core particles having a surface covered by nanoparticles; additives selected from compounds having functional groups selected from: organic carboxylic acids, amino acids, amide carboxylic acids, N-acyl amino acids, and their salts; organic sulfonic acids and their salts; organic phosphonic acids and their salts; polymeric carboxylic acids and their salts; polymeric sulfonic acids and their salts; polymeric phosphonic acids and their salts; arylamines, amino alcohols, aliphatic amines, heterocyclic amines, isohydroxamic acids, substituted phenols, sulfonamides, thiols, polyols having hydroxyl groups; and combinations thereof; a pH adjuster selected from sodium hydroxide, potassium hydroxide, cesium hydroxide, ammonium hydroxide, organic quaternary ammonium hydroxide, and combinations thereof; and the remainder being water; wherein the core particles are selected from silicon dioxide, alumina, titanium dioxide, zirconium oxide, polymer particles, and combinations thereof; and the nanoparticles are selected from nanoparticles of compounds of zirconium, titanium, iron, manganese, zinc, cerium, yttrium, calcium, magnesium, fluorine, lanthanum, and strontium, and combinations thereof. Both silica and alumina are core particles and do not have a coating effect.

[0005] Silicon powder, as an inexpensive source of elemental silicon, is chemically inert and therefore difficult to use directly in liquid-phase coating processes. Currently, there is no effective method to directly utilize silicon powder to achieve uniform silica coating on alumina surfaces via wet chemical processes. Developing preparation technologies using silicon powder as a raw material is of great significance, as it can significantly reduce costs and enable the construction of high-performance core-shell structures. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a composite abrasive for polishing nano-silica-alumina, overcoming the shortcomings of existing technologies. This method utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and silica, respectively. Through an in-situ oxidation-hydrolysis strategy, a uniform and robust silica coating layer is prepared on the surface of existing alumina micropowder. This method is simple, low-cost, and suitable for industrial production. This abrasive is suitable for surface planarization polishing of semiconductor wafers (such as silicon wafers and sapphire substrates).

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a composite abrasive for polishing with nano-silica-alumina utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and silica, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The method includes preparing sheet-like alumina, preparing silica from a desilication solution, activating the alumina core, pretreating the silica powder, in-situ oxidation-hydrolysis coating reaction, and post-treatment. The specific steps are as follows:

[0009] 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing, the pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol in a certain proportion, and after stirring, sonication and drying, flake alumina is obtained.

[0010] 2) Preparation of silica from desiliconization solution: The silicon-containing gas generated by high-temperature calcination in step 1) is passed into water to form a silicon-containing solution, which is the desiliconization solution. Ammonia water is then added to adjust the pH value, and the solution is heated and stirred, filtered, concentrated by heating, and freeze-dried to obtain silica.

[0011] 3) Activation of alumina core: The flake alumina obtained in step 1) is dispersed in water, ultrasonically stirred, and the surface hydroxyl density is increased by acid and alkali etching. After washing, it is ready for use.

[0012] 4) Pretreatment of silicon powder: The silicon dioxide obtained in step 2) is subjected to ball milling or air jet milling to reduce its particle size to the submicron level, thereby increasing the specific surface area and reactivity.

[0013] 5) In-situ oxidation-hydrolysis coating reaction: The activated alumina dispersion from step 3) and the pretreated silicon powder from step 4) are mixed in a certain proportion, and the mixture is thoroughly mixed and evenly dispersed by high-energy ultrasonic treatment to form a stable suspension. The mixed suspension is transferred to a high-pressure reactor, and an oxidant and a catalyst are added. The oxidant is any one or both of 68 wt% nitric acid and 30 wt% hydrogen peroxide. The catalyst is 10 wt% ammonia water. The reactor is sealed and heated with stirring.

[0014] 6) Post-processing: After the reaction is completed, cool to room temperature, take out the product, collect the solid product by centrifugation or filtration, wash repeatedly with deionized water until neutral, and then dry and calcined to finally obtain the nano-silica-alumina polishing composite abrasive product.

[0015] Furthermore, in step 1), the alkaline washing pretreatment process uses a NaOH solution with a concentration of 2–8 mol / L and a liquid-to-solid ratio of 2–6 mL / g. Heating is performed in a homogeneous reactor at a temperature of 60–120°C, a holding time of 100–200 min, and a rotation speed of 50–200 r / min. The ultrasonic power is 300–500 W, and the ultrasonic time is 20–40 min. The calcination heating rate is 5–10°C / min, the vacuum calcination temperature is 1000–1300°C, the holding time is 30–180 min, and the vacuum degree is 10. - 3 At a flow rate of 100–200 mL / min, the length of the alumina obtained was 2–10 μm.

[0016] Furthermore, in step 2), the ammonia concentration is 5–15 wt%, the pH value of the precipitation reaction is controlled at 7–11, the heating and stirring reaction temperature is 50–90℃, the heating and stirring reaction time is 0.5–2 h, and the stirring speed is 30–300 r / min; 100–300 ml of deionized water is added during filtration, and the filtration time is 10–40 min; the heating and concentration uses a DF-101SS heat-collecting magnetic stirrer, the heating temperature is 40–80℃, the stirring speed is set to 50–150 rpm / min, and the solution is freeze-dried and recovered at -10–5℃ after evaporation.

[0017] Furthermore, in step 3), the mass ratio of flake alumina to water is 1:20, ultrasonic stirring is performed for 30-60 minutes, stirring and heating is carried out at pH 2-4 or 11-13, the pH is adjusted with acetic acid or ammonia, the heating temperature is 45-85℃, and the heating time is 1.5-5 hours. After treatment, the hydroxyl density on the surface of the flake alumina is 15-25 hydroxyl groups / nm. 2 .

[0018] Furthermore, in step 4), the silicon powder is subjected to ball milling or air jet milling to reduce the particle size to the submicron level of 100–500 nm and the specific surface area to 150–400 m². 2 / g, significantly improving reactivity.

[0019] Furthermore, in step 5), the activated alumina dispersion is mixed with the pretreated silicon powder at a weight ratio of Al2O3:Si = 1:0.2 to 1:1; the high-energy ultrasonic treatment is performed with an ultrasonic power of 500 to 1000 W for 1 to 2 hours; 3 to 5 ml / 100 g of oxidant and 8 to 12 ml / 100 g of catalyst are added, and the mixture is heated to 180-220°C under stirring in a sealed reactor and kept at that temperature for 12 to 48 hours.

[0020] Furthermore, in step 6), drying is carried out at 80-120℃ for 1-2 hours, and calcination is carried out at 500-700℃ for 1-3 hours.

[0021] Furthermore, the mixing ratio of the solid obtained in step 1) to ethanol is 1g:10-20ml.

[0022] Furthermore, the physicochemical characteristics of the solid waste fly ash from the coal-fired power plant are as follows: particle size is 75-100 μm, effective components by weight percentage are: Al2O3 38%-42%, SiO2 35%-45%, main impurity components by weight percentage are: Fe2O3 2%-6%, CaO 1%-4%, MgO 0.5%-2%, K2O 1%-3%, Na2O 0.5%-2%, and the remainder are other impurities.

[0023] Furthermore, the physicochemical properties and composition range of the desilication solution are as follows: pH value of 2-4, density of 1.05-1.15 g / cm³. 3 The main components, by weight percentage, are: H2SiF 63%–8%, HF 0.5%–2%, and H2O 88%–95%. It also contains the main impurities: AlF 30.1%–0.5%, FeF 30.05%–0.2%, with the remainder being other impurities.

[0024] The reaction mechanism of this invention is as follows: In a high-temperature, high-pressure alkaline oxidizing environment, the surface of silicon powder is oxidized to form amorphous silicon dioxide (SiO2). This silicon dioxide layer then dissolves to generate highly reactive silicate ions, H3SiO4- or H2SiO4-. 2 These active silicon particles are present in extremely high concentrations near the surface of alumina, and will immediately undergo heterogeneous nucleation and deposition at the active sites on the alumina surface, thereby achieving in-situ coating. This process inhibits the homogeneous nucleation of silicate ions, ensuring preferential coating.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1) This invention uses coal-based solid waste fly ash as raw material to directionally generate high-purity flaky α-Al2O3 crystals in the fly ash matrix. The aluminum (Al2O3) and silicon (SiO2) elements in the fly ash are converted into alumina and nano-silica, respectively, achieving efficient separation of silicon and aluminum elements and in-situ removal of hematite impurities, thus realizing efficient separation and utilization of aluminum and silicon dual resources.

[0027] 2) It realizes the resource recovery of fluorine-containing exhaust gas, solves the environmental pollution problem of fluorine exhaust gas, and reduces the environmental burden;

[0028] 3) Innovative raw materials and low cost: It enables the use of inexpensive and readily available elemental silicon powder to replace expensive silicates, silica sols or silanes as silicon sources, which greatly reduces production costs;

[0029] 4) The process is unique and innovative, using a high-temperature and high-pressure alkaline oxidation environment, which solves the problem of the chemical inertness of silicon powder and realizes the "in-situ" conversion and coating from elemental silicon to active silicon in one step;

[0030] 5) Good coating effect: The "in-situ" reaction mechanism results in a high local concentration of silicon powder on the alumina surface, high coating efficiency, uniform and dense shell, and strong bonding with the core.

[0031] 6) It is environmentally friendly, avoiding the use of toxic silane precursors, and the process is relatively green. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the specific embodiments used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some embodiments of the present invention. For those skilled in the art, other specific embodiments can be obtained based on these specific embodiments without creative effort.

[0034] The components of the embodiments of the invention described and shown in the specific embodiments herein can be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the specific embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0035] The physicochemical properties of fly ash from coal-fired power plants in Examples 1-3 are as follows: particle size 75-100 μm; effective components by weight percentage: Al₂O₃ 38%-42%, SiO₂ 35%-45%; main impurities by weight percentage: Fe₂O₃ 2%-6%, CaO 1%-4%, MgO 0.5%-2%, K₂O 1%-3%, Na₂O 0.5%-2%, with the remainder being other impurities. The physicochemical properties and composition range of the desilication solution are: pH value 2-4, density 1.05-1.15 g / cm³. 3 The main components, by weight percentage, are: H2SiF 63%–8%, HF 0.5%–2%, and H2O 88%–95%. It also contains the main impurities: AlF 30.1%–0.5%, FeF 30.05%–0.2%, with the remainder being other impurities.

[0036] Example 1

[0037] A method for preparing a composite abrasive for polishing with nano-silica and alumina utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and nano-silica, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The method includes preparing sheet-like alumina, preparing silica from a desilication solution, activating the alumina core, pretreating the silica powder, in-situ oxidation-hydrolysis coating reaction, and post-treatment. The specific steps are as follows:

[0038] 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing to enhance the activity of internal silicon and aluminum components. The pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol at a ratio of 1g:10ml. After stirring, sonication, and drying, flake alumina is obtained.

[0039] The alkaline washing pretreatment process uses a 2 mol / L NaOH solution with a liquid-to-solid ratio of 3 mL / g, heated in a homogeneous reactor at 60℃ for 100 min at a rotation speed of 50 r / min. Vacuum calcination is performed at a heating rate of 5℃ / min, a calcination temperature of 1100℃, a holding time of 60 min, and a vacuum degree of 10. -3 Pa, nitrogen flow rate is 100 mL / min, nitrogen gas has the following functions: on the one hand, to create an inert atmosphere to prevent the material from being oxidized during calcination and to ensure the smooth progress of solid-phase reaction; on the other hand, it can carry the fluorine-containing gas generated during calcination, which is convenient for the subsequent resource recovery of fluorine-containing tail gas. The length of the obtained alumina is 2 to 10 μm.

[0040] 2) Preparation of nano-silica from desilication solution: The gas generated by high-temperature calcination in step 1) is passed into water, then ammonia is added, and the precipitation reaction is completed by low-temperature stirring. After filtration and freeze-drying, nano-silica is obtained. The ammonia concentration is 5wt%, and the pH value of the precipitation reaction is controlled at 7. The reaction temperature is 50℃, the reaction time is 0.5h, and the stirring speed is 50r / min. 100ml of deionized water is added during filtration, and the filtration time is 15min. For heating and concentration, a DF-101SS heat-collecting magnetic stirrer is used, with a heating temperature of 60℃ and a stirring speed of 50rpm / min. After the solution evaporates, it is freeze-dried at 0℃ for recovery.

[0041] 3) Activation of alumina cores: Take 10g of α-alumina powder with an average particle size of 0.5μm, add 200mL of deionized water, and sonicate for 60min. Adjust the pH to 3 with acetic acid, and activate by stirring at 70℃ for 4 hours. Wash until neutral, redisperse in 200mL of deionized water. After treatment, the hydroxyl density on the surface of the flake alumina is 15-25 hydroxyl groups / nm. 2 ;

[0042] 4) Pretreatment of silicon powder: Take 6g of silicon powder with a particle size of approximately 300nm (obtained by ball milling), achieving a specific surface area of ​​150-400m². 2 / g, significantly improved reactivity, added to the above alumina dispersion. Sonicated at 600W for 90 minutes to form a mixed suspension;

[0043] 5) In-situ oxidation-hydrolysis coating reaction: The activated alumina dispersion from step 3) and the pretreated silicon powder from step 4) are mixed at a weight ratio of Al2O3:Si = 1:0.6. The mixture is then subjected to high-energy ultrasonic treatment (1000W power, 1-2 hours) to ensure thorough mixing and uniform dispersion, forming a stable suspension. The suspension is transferred to a 500mL high-pressure reactor, and 0.065mL of 68wt% nitric acid (as an oxidant) and 0.16mL of 10wt% ammonia (to create an alkaline environment and catalyze) are added. The reactor is sealed, stirred at 200rpm, heated to 200℃, and reacted for 24 hours.

[0044] 6) Post-processing: After natural cooling, the product is collected by centrifugation, washed three times with water and ethanol, and dried at 100℃. The dried powder is calcined at 600℃ for 2 hours to obtain the final nano-silica-alumina composite abrasive product for polishing.

[0045] Example 2

[0046] A method for preparing a composite abrasive for polishing with nano-silica and alumina utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and nano-silica, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The method includes preparing sheet-like alumina, preparing silica from a desilication solution, activating the alumina core, pretreating the silica powder, in-situ oxidation-hydrolysis coating reaction, and post-treatment. The specific steps are as follows:

[0047] 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing to enhance the activity of internal silicon and aluminum components. The pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol at a ratio of 1g:20ml. After stirring, sonication, and drying, flake alumina is obtained.

[0048] The alkaline washing pretreatment process uses a 5 mol / L NaOH solution with a liquid-to-solid ratio of 3 mL / g, heated in a homogeneous reactor at 60℃ for 120 min at a rotation speed of 100 r / min. Vacuum calcination is performed at a heating rate of 8℃ / min, a calcination temperature of 1200℃, a holding time of 120 min, and a vacuum degree of 10. -3 Pa, nitrogen flow rate is 150 mL / min, nitrogen gas has the following functions: on the one hand, to create an inert atmosphere to prevent the material from being oxidized during calcination and to ensure the smooth progress of solid-phase reaction; on the other hand, it can carry the fluorine-containing gas generated during calcination, which is convenient for the subsequent resource recovery of fluorine-containing tail gas. The length of the obtained alumina is 2 to 10 μm.

[0049] 2) Preparation of nano-silica from desilication solution: The gas generated by high-temperature calcination in step 1) is passed into water, then ammonia is added, and the precipitation reaction is completed by low-temperature stirring. After filtration and freeze-drying, nano-silica is obtained. The ammonia concentration is 8 wt%, and the pH value of the precipitation reaction is controlled at 9. The reaction temperature is 75℃, the reaction time is 1 h, and the stirring speed is 60 r / min. 300 ml of deionized water is added during filtration, and the filtration time is 40 min. For heating and concentration, a DF-101SS heat-collecting magnetic stirrer is used, with a heating temperature of 40℃ and a stirring speed of 100 rpm / min. After the solution evaporates, it is freeze-dried at -5℃ for recovery.

[0050] 3) Activation of alumina cores: Take 10g of α-alumina powder with an average particle size of 0.5μm, add 200mL of deionized water, and sonicate for 40min. Adjust the pH to 12 with ammonia water, and activate by stirring at 55℃ for 2.5h. Wash until neutral, redisperse in 200mL of deionized water. After treatment, the hydroxyl density on the surface of the flake alumina is 15-25 hydroxyl groups / nm. 2 ;

[0051] 4) Pretreatment of silicon powder: Take 2g of silicon powder with a particle size of approximately 300nm (obtained by ball milling), achieving a specific surface area of ​​150-400m². 2 / g, significantly improved reactivity, was added to the above alumina dispersion. The mixture was ultrasonically treated at 700 kW for 60 minutes to form a mixed suspension;

[0052] 5) In-situ oxidation-hydrolysis coating reaction: The activated alumina dispersion from step 3) and the pretreated silicon powder from step 4) are mixed at a weight ratio of Al2O3:Si = 1:0.2. The mixture is then subjected to high-energy ultrasonic treatment (500W power, 1-2 hours) to ensure thorough mixing and uniform dispersion, forming a stable suspension. The suspension is transferred to a 500mL high-pressure reactor, and 0.05mL of 30wt% hydrogen peroxide (as an oxidant) and 0.11mL of 10wt% ammonia (to create an alkaline environment and catalyze) are added. The reactor is sealed, stirred at 200rpm, and heated to 220℃ for 18 hours.

[0053] 6) Post-processing: After natural cooling, the product is collected by centrifugation, washed three times with water and ethanol, and dried at 120℃. The dried powder is calcined at 500℃ for 2 hours to obtain the final nano-silica-alumina composite abrasive product for polishing.

[0054] Example 3

[0055] A method for preparing a composite abrasive for polishing with nano-silica and alumina utilizes aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, to convert them into alumina and nano-silica, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The method includes preparing sheet-like alumina, preparing silica from a desilication solution, activating the alumina core, pretreating the silica powder, in-situ oxidation-hydrolysis coating reaction, and post-treatment. The specific steps are as follows:

[0056] 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing to enhance the activity of internal silicon and aluminum components. The pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol at a ratio of 1g:15ml. After stirring, sonication, and drying, flake alumina is obtained.

[0057] The alkaline washing pretreatment process uses an 8 mol / L NaOH solution with a liquid-to-solid ratio of 6 mL / g, heated in a homogeneous reactor at 120℃ for 200 min at a rotation speed of 200 r / min. Vacuum calcination is performed at a heating rate of 8℃ / min, a calcination temperature of 1300℃, a holding time of 30 min, and a vacuum degree of 10. -3Pa, nitrogen flow rate is 200 mL / min, nitrogen gas has the following functions: on the one hand, to create an inert atmosphere to prevent the material from being oxidized during calcination and to ensure the smooth progress of solid-phase reaction; on the other hand, it can carry the fluorine-containing gas generated during calcination, which is convenient for the subsequent resource recovery of fluorine-containing tail gas. The length of the obtained alumina is 2 to 10 μm.

[0058] 2) Preparation of nano-silica from desilication solution: The gas generated by high-temperature calcination in step 1) is passed into water, then ammonia is added, and the precipitation reaction is completed by low-temperature stirring. After filtration and freeze-drying, nano-silica is obtained. The ammonia concentration is 15wt%, and the pH value of the precipitation reaction is controlled at 11. The reaction temperature is 90℃, the reaction time is 2h, and the stirring speed is 300r / min. 300ml of deionized water is added during filtration, and the filtration time is 40min. For heating and concentration, a DF-101SS heat-collecting magnetic stirrer is used, with a heating temperature of 80℃ and a stirring speed of 150rpm / min. After the solution evaporates, it is freeze-dried at -10℃ for recovery.

[0059] 3) Activation of alumina cores: Take 10g of α-alumina powder with an average particle size of 0.5μm, add 200mL of deionized water, and sonicate for 60min. Adjust the pH to 4 with acetic acid, and activate by stirring at 85℃ for 1.5h. Wash until neutral, redisperse in 200mL of deionized water. After treatment, the hydroxyl density on the surface of the flake alumina is 15-25 hydroxyl groups / nm. 2 ;

[0060] 4) Pretreatment of silicon powder: Take 10g of silicon powder with a particle size of approximately 500nm (obtained by ball milling), achieving a specific surface area of ​​150-400m². 2 / g, significantly improved reactivity, was added to the above alumina dispersion. The mixture was ultrasonically treated at 1000 power for 120 minutes to form a mixed suspension;

[0061] 5) In-situ oxidation-hydrolysis coating reaction: The activated alumina dispersion from step 3) and the pretreated silicon powder from step 4) are mixed at a weight ratio of Al2O3:Si = 1:1. The mixture is then subjected to high-energy ultrasonic treatment (800W) for 1-2 hours to ensure thorough mixing and uniform dispersion, forming a stable suspension. The suspension is transferred to a 500mL high-pressure reactor, and 0.095mL of 30wt% hydrogen peroxide (as an oxidant) and 0.21mL of 10wt% ammonia (to create an alkaline environment and catalyze) are added. The reactor is sealed, stirred at 200rpm, and heated to 180℃ for 48 hours.

[0062] 6) Post-processing: After natural cooling, the product is collected by centrifugation, washed three times with water and ethanol, and dried at 100℃. The dried powder is calcined at 700℃ for 1.5 hours to obtain the final nano-silica-alumina composite abrasive product for polishing.

[0063] Table 1 shows the performance comparison data of the composite abrasive products obtained in Examples 1-3 of this invention and the products in Comparative Examples 1-3.

[0064] Table 1

[0065]

[0066] Table 1 is a performance comparison table designed to verify the advantages of the core-shell structure abrasive of the present invention (Examples 1-3) over traditional abrasives (Comparative Examples 1-3). It quantifies and compares several key indicators (such as abrasive type, average particle size, Mohs hardness, material removal rate, surface roughness, and number of scratches), highlighting the comprehensive performance improvement of the core-shell structure design during the polishing process. Specifically, Table 1 demonstrates that the abrasive of the present invention, while maintaining a high material removal rate, can significantly improve surface quality (such as reducing roughness and scratches), thus possessing potential application value in precision polishing fields such as semiconductors and optics. The more advanced indicators of Examples 1-3 of the present invention are described below:

[0067] As can be seen from the data in Table 1, the embodiments of the present invention are more advanced in the following aspects:

[0068] Surface roughness Ra (nm): The values ​​of the examples (0.19-0.25nm) are significantly lower than those of Comparative Example 1 (0.45nm) and Comparative Example 2 (0.55nm), indicating that core-shell abrasives can produce smoother surfaces and reduce microscopic defects.

[0069] Number of scratches (scratches / wafer): The value of the example (1-2 scratches) is much lower than that of Comparative Example 1 (10-15 scratches) and Comparative Example 2 (>20 scratches), indicating that the core-shell structure abrasive causes less damage to the workpiece during polishing and improves the yield.

[0070] Material removal rate (nm / min): The value of the example (270-295nm / min) is slightly lower than that of Comparative Example 1 (260nm / min) and Comparative Example 2 (310nm / min). However, considering the low roughness and fewer scratches, the example achieves a better balance between efficiency and surface quality, and has better overall performance.

[0071] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a composite abrasive for polishing with nano-silica-alumina, characterized in that, Aluminum and silicon elements in fly ash, a solid waste from coal-fired power plants, are converted into alumina and silicon dioxide, respectively, achieving efficient separation and utilization of both aluminum and silicon resources. The process includes preparing flake alumina, preparing silicon dioxide from desilication liquid, activating alumina cores, pretreating silicon powder, in-situ oxidation-hydrolysis coating reaction, and post-treatment. Specific steps are as follows: 1) Preparation of flake alumina: Solid waste fly ash is pretreated by alkaline washing, the pretreated fly ash is ground and mixed with ammonium fluoride, and then calcined under vacuum to complete the solid-phase reaction. After cooling to room temperature, the resulting solid is mixed with ethanol in a certain proportion, and after stirring, sonication and drying, flake alumina is obtained. 2) Preparation of silica from desiliconization solution: The silicon-containing gas generated by high-temperature calcination in step 1) is passed into water to form a silicon-containing solution, which is the desiliconization solution. Ammonia water is then added to adjust the pH value, and the solution is heated and stirred, filtered, concentrated by heating, and freeze-dried to obtain silica. 3) Activation of alumina core: The flake alumina obtained in step 1) is dispersed in water, ultrasonically stirred, and the surface hydroxyl density is increased by acid and alkali etching. After washing, it is ready for use. 4) Pretreatment of silicon powder: The silicon dioxide obtained in step 2) is subjected to ball milling or air jet milling to reduce its particle size to the submicron level, thereby increasing the specific surface area and reactivity. 5) In-situ oxidation-hydrolysis coating reaction: The activated alumina dispersion from step 3) and the pretreated silicon powder from step 4) are mixed in a certain proportion, and the mixture is thoroughly mixed and evenly dispersed by high-energy ultrasonic treatment to form a stable suspension. The mixed suspension is transferred to a high-pressure reactor, and an oxidant and a catalyst are added. The oxidant is any one or both of 68 wt% nitric acid and 30 wt% hydrogen peroxide. The catalyst is 10 wt% ammonia water. The reactor is sealed and heated with stirring. 6) Post-processing: After the reaction is completed, cool to room temperature, take out the product, collect the solid product by centrifugation or filtration, wash repeatedly with deionized water until neutral, and then dry and calcined to finally obtain the nano-silica-alumina polishing composite abrasive product.

2. The method for preparing a nano-silica-alumina composite abrasive for polishing according to claim 1, characterized in that, In step 1), the alkaline washing pretreatment process involves using a 2-8 mol / L NaOH solution with a liquid-to-solid ratio of 2-6 mL / g, heated in a homogeneous reactor at a temperature of 60-120°C for 100-200 min at a rotation speed of 50-200 r / min; the ultrasonic power is 300-500 W for 20-40 min; the calcination process involves a heating rate of 5-10°C / min, a vacuum calcination temperature of 1000-1300°C, a holding time of 30-180 min, and a vacuum degree of 10. -3 At a flow rate of 100–200 mL / min, the length of the alumina obtained was 2–10 μm.

3. The method for preparing a composite abrasive for polishing nano-silica-alumina according to claim 1, characterized in that, In step 2), the ammonia concentration is 5-15 wt%, the pH of the precipitation reaction is controlled at 7-11, the heating and stirring reaction temperature is 50-90℃, the heating and stirring reaction time is 0.5-2h, and the stirring speed is 30-300 r / min. During filtration, 100-300 ml of deionized water is added, and the filtration time is 10-40 min. For heating and concentration, a DF-101SS heat-collecting magnetic stirrer is used, with a heating temperature of 40-80℃ and a stirring speed of 50-150 rpm / min. After the solution evaporates, it is freeze-dried and recovered at -10 to 5℃.

4. The method for preparing a composite abrasive for polishing nano-silica-alumina according to claim 1, characterized in that, In step 3), the mass ratio of flake alumina to water is 1:

20. The alumina is ultrasonically stirred for 30-60 minutes, heated while stirring at pH 2-4 or 11-13, and the pH is adjusted with acetic acid or ammonia. The heating temperature is 45-85℃, and the heating time is 1.5-5 hours. After treatment, the hydroxyl group density on the surface of the flake alumina is 15-25 hydroxyl groups / nm. 2 .

5. The method for preparing a composite abrasive for polishing nano-silica-alumina according to claim 1, characterized in that, Step 4) involves ball milling or air jet milling of the silicon powder to reduce the particle size to the submicron level of 100–500 nm and the specific surface area to 150–400 nm. 2 / g, significantly improving reactivity.

6. The method for preparing a nano-silica-alumina composite abrasive for polishing according to claim 1, characterized in that, In step 5), the activated alumina dispersion is mixed with the pretreated silicon powder at a weight ratio of Al2O3:Si = 1:0.2 to 1:1; the high-energy ultrasonic treatment is performed with an ultrasonic power of 500 to 1000W for 1 to 2 hours; 3 to 5 ml / 100g of oxidant and 8 to 12 ml / 100g of catalyst are added, and the mixture is heated to 180-220℃ in a sealed reactor under stirring and kept at that temperature for 12 to 48 hours.

7. The method for preparing a nano-silica-alumina composite abrasive for polishing according to claim 1, characterized in that, In step 6), drying is carried out at 80-120℃ for 1-2 hours, and calcination is carried out at 500-700℃ for 1-3 hours.

8. The method for preparing a composite abrasive for polishing nano-silica-alumina according to claim 1, characterized in that, The mixing ratio of the solid obtained in step 1) to ethanol is 1g:10-20ml.

9. The method for preparing a nano-silica-alumina composite abrasive for polishing according to claim 1, characterized in that, The physicochemical characteristics of the solid waste fly ash from the coal-fired power plant are as follows: particle size is 75-100 μm, effective components by weight percentage are: Al2O3 38%-42%, SiO2 35%-45%, main impurity components by weight percentage are: Fe2O3 2%-6%, CaO 1%-4%, MgO 0.5%-2%, K2O 1%-3%, Na2O 0.5%-2%, and the remainder are other impurities.

10. The method for preparing a nano-silica-alumina composite abrasive for polishing according to claim 1, characterized in that, The physicochemical properties and composition range of the desilication solution are as follows: pH value of 2-4, density of 1.05-1.15 g / cm³. 3 The main components, by weight percentage, are: H2SiF 63%–8%, HF 0.5%–2%, and H2O 88%–95%. It also contains the main impurities: AlF 30.1%–0.5%, FeF 30.05%–0.2%, with the remainder being other impurities.

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