A method for preparing spherical silicon fine powder

Abstract

The application belongs to the technical field of inorganic nonmetallic material preparation, and particularly relates to a preparation method of spherical silicon micro powder. The method comprises a pretreatment method of a silicic acid precursor, and the pretreatment method comprises the following steps: freezing a silicic acid solution with a concentration of 5wt% to 8wt%, forming a solid ice body, then thawing and performing solid-liquid separation to obtain a silica precursor filter cake; and performing calcination treatment on the silica precursor filter cake in an oxidation atmosphere at 900 DEG C to 1000 DEG C to obtain a silica precursor powder. The method effectively solves the hard agglomeration problem of the silicic acid precursor in the dehydration process, and removes impurities such as alkali metals. The precursor powder is subjected to subsequent crushing, modification and flame melting and spheroidization processes to obtain spherical silicon micro powder which meets the requirements of 4N purity (SiO2 >= 99.99%) and high sphericity (>= 0.95) at the same time, and the spherical silicon micro powder is suitable for high-end electronic packaging and other fields.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic material preparation technology, specifically relating to a method for preparing spherical silicon micropowder. Background Technology

[0002] Spherical silicon micropowder is a core material in high-end electronic packaging, specialty coatings, and other fields. Its purity and sphericity determine the performance of downstream products. High-temperature melt spheroidization is a key technology for preparing products with high sphericity, but the compatibility of raw materials is a bottleneck for its industrialization.

[0003] Currently, raw material systems are mainly divided into three categories. The first category is halosilanes, which have high purity but huge costs and safety risks. The second category is minerals / silicates, which have low cost but high impurity content, require complex wet purification, and face great environmental pressure. The third category is silicic acid, which, as a high-purity precursor, has a wide range of sources and is considered an ideal raw material.

[0004] However, the use of silicic acid in the melt spheroidizing method has a long-standing inherent contradiction that has not been systematically resolved. During the conventional dehydration process, the silanol groups (Si-OH) on the surface of silicic acid (or the silica gel formed from it) are prone to irreversible condensation reactions, forming "hard agglomerates" with strong internal bonds and irregular morphology. These hard agglomerates cause two problems in the subsequent melt spheroidizing process at temperatures exceeding 1700°C: firstly, impurities encapsulated inside the agglomerates are difficult to completely remove during instantaneous melting, affecting the final purity; secondly, the agglomerates themselves may not be completely melted, or their anisotropy may result in irregular spherical shapes and rough surfaces after melting, severely restricting the sphericity of the product.

[0005] While existing technologies have attempted improvements, such as employing spray drying, the rapid dehydration process in spray drying leads to intense condensation of silanol groups, resulting in more severe hard agglomerates and irregular morphology in subsequent spheroidized products. Furthermore, spray drying requires the evaporation of large amounts of water, resulting in high energy consumption and poor economic efficiency. It also fails to specifically prepare precursors with high thermal stability and low agglomeration tendency for high-temperature melt spheroidization. Simple process combinations cannot resolve the core contradiction of "hard agglomerates leading to poor melt quality."

[0006] Therefore, developing a dedicated pretreatment method that can effectively deconstruct the native agglomeration of silica precursors at the molecular / particle level and simultaneously impart excellent high-temperature thermal stability is a key technological bottleneck for achieving large-scale production of 4N-grade spherical silica micropowder. Summary of the Invention

[0007] The primary objective of this invention is to overcome the inherent defects of silica precursors during melt spheroidization, where hard agglomeration and thermal instability make it difficult to simultaneously achieve both sphericity and purity. To achieve this objective, this invention provides a dedicated "deagglomeration-stabilization" composite pretreatment method, as well as a process for preparing spherical silica micropowder incorporating this method. This preparation process, through the synergy of physical and chemical means, fundamentally modifies the microstructure of the silica precursor, making it suitable for high-quality melt spheroidization, thereby stably and continuously producing spherical silica micropowder that simultaneously meets the requirements of 4N-grade purity (SiO2 ≥ 99.99%) and high sphericity (≥ 0.95).

[0008] On one hand, the present invention provides a method for pretreatment of silica precursors for preparing spherical silica micropowder, the method comprising the following steps:

[0009] S1. Depolymerization treatment: A silica solution with a concentration of 5wt% to 8wt% is frozen to form a solid ice body, then thawed and subjected to solid-liquid separation to obtain a silica precursor filter cake.

[0010] S2. Stabilization treatment: The silica precursor filter cake obtained in step S1 is subjected to a baking treatment in an oxidizing atmosphere at 900℃~1000℃ to obtain silica precursor powder.

[0011] Furthermore, in the silicic acid precursor pretreatment method, in step S1, the pH value of the silicic acid solution is 3.0~4.0.

[0012] Furthermore, in the silica precursor pretreatment method, in step S1, the freezing temperature is -25℃ to -45℃, and the thawing temperature is 35℃ to 45℃.

[0013] On the other hand, a method for preparing spherical silica micropowder is also provided, comprising: treating silica raw materials with the silica precursor pretreatment method described in this invention to obtain silica precursor powder, and performing melt spheroidization treatment on the silica precursor powder to obtain spherical silica micropowder.

[0014] Furthermore, the preparation method further includes, before the melt spheroidization treatment, performing air jet milling and classification on the silica precursor powder to obtain silica micro powder with a particle size of 1μm~20μm.

[0015] Furthermore, the preparation method further includes: performing a first surface modification on the silica micropowder after the airflow pulverization and classification and before the melt spheroidization treatment.

[0016] Furthermore, in the preparation method, the melt spheroidizing treatment is flame melt spheroidizing, the temperature of the flame melt spheroidizing is 1900℃~2000℃, and the material residence time is 1.0 second~1.2 seconds.

[0017] Furthermore, in the preparation method, after the melt spheroidization treatment, a second surface modification is performed on the obtained spherical silica powder crude product.

[0018] Furthermore, in the preparation method, the spheroidized product is subjected to airflow classification to obtain spherical silicon micropowder with a particle size of 1~20μm.

[0019] Finally, the present invention also provides spherical silicon micropowder prepared by the method of the present invention, wherein the spherical silicon micropowder has a SiO2 mass content ≥99.99%, a sphericity ≥0.95, and a particle size of 1~20μm.

[0020] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0021] (1) By first breaking down the silica gel network through "freezing-thawing-solid-liquid separation" (depolymerization), and then deeply removing residual silanol groups through "high-temperature baking" (stabilization), the irreversible hard agglomeration caused by conventional dehydration (such as spray drying) is avoided from the source. This results in the prepared silica precursor powder having a loose, low agglomeration tendency physical structure and high thermal stability. In the subsequent instantaneous melting and spheroidization process exceeding 1900℃, it can fully melt and uniformly spheroidize, thereby significantly improving the sphericity (up to 95%) and spheroidization rate of the final product. This synergistic process systematically overcomes the hard agglomeration and thermal instability problems of silica precursors in the prior art, which cannot be achieved by simple combination processes in the prior art.

[0022] (2) Due to the fundamental modification of the silica precursor, the spherical silica powder prepared by the method of the present invention has an order-of-magnitude improvement in spherical formation rate (>95%) and sphericity qualification rate (≥0.95% >90%) compared with the traditional pretreatment method, and the product purity is stable at 4N level.

[0023] (3) The pretreatment process parameters (such as freezing-thawing, specific sand baking temperature) are optimized and determined for the specific purpose of “preparing silica precursors for melt spheroidization”. Their mechanism and effect are fundamentally different from the freezing or heat treatment technology used in other fields (such as catalyst carriers, adsorbents).

[0024] (4) This pretreatment process does not require repeated washing with large amounts of acid and alkali, thus avoiding the generation of high-salt wastewater. The final product has excellent overall performance and high application value. It is especially suitable for high-end electronic packaging, special thermally conductive adhesives, high-performance composite materials and other fields. Attached Figure Description

[0025] Figure 1 Microscopic image of the spherical silica powder prepared in Example 1.

[0026] Figure 2 Microscopic image of the spherical silica powder prepared in Example 2.

[0027] Figure 3 The image shows a scanning electron microscope (SEM) image of the spherical silicon micropowder prepared for Comparative Example 1.

[0028] Figure 4 The image shows a scanning electron microscope (SEM) image of the spherical silicon micropowder prepared for Comparative Example 2.

[0029] Figure 5 The particle size distribution diagram of silica micropowder prepared by airflow milling and classification in Example 1.

[0030] Figure 6 The particle size distribution diagram is shown for the silica micropowder prepared by airflow milling and classification in Example 2.

[0031] Figure 7 The particle size distribution of silica micropowder prepared by air jet milling and classification is shown in Comparative Example 1.

[0032] Figure 8 The particle size distribution of silica micropowder prepared by air jet milling and classification is shown in Comparative Example 2.

[0033] Figure 9 The particle size distribution diagram is shown for the spherical silica powder prepared in Example 1.

[0034] Figure 10 The particle size distribution diagram is shown for the spherical silicon micropowder prepared in Example 2.

[0035] Figure 11 The particle size distribution diagram is shown for the spherical silica powder prepared in Comparative Example 1.

[0036] Figure 12 The particle size distribution diagram is for the spherical silica powder prepared in Comparative Example 2. Detailed Implementation

[0037] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0038] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0039] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0040] Example 1

[0041] In this embodiment, spherical silica powder was prepared using sodium silicate as the raw material.

[0042] S1. Raw material preparation: A 20wt% sodium silicate solution was passed through an ion exchange resin column at a flow rate of 2 m / h for ion exchange (exchange temperature 30℃) to obtain a high-purity silicic acid solution. The solution concentration was approximately 5wt%, the pH value was 3.0, and the conductivity was approximately 25 μS / cm.

[0043] S2. Freezing treatment: The high-purity silica solution obtained in S1 is sent to a solidification device and kept at a constant temperature of -30℃ (temperature fluctuation ±1℃) for 4 hours to form a uniform solid ice body.

[0044] S3. Thawing treatment: Transfer the solid ice to a liquefaction device and treat it at 45°C for 4 hours to obtain a suspension containing silica precipitate.

[0045] S4. Solid-liquid separation: The suspension containing silica precipitate obtained in S3 is subjected to negative pressure filtration at an operating pressure of -0.04 MPa for 1 hour to obtain a filter cake with a water content of 20%.

[0046] S5. Fluidized bed drying: Place the filter cake in a fluidized bed drying device and dry it at 180°C for 3 hours to obtain a preliminarily dried powder with a moisture content of 20%.

[0047] S6. High-temperature baking: The pre-dried powder is placed in a baking furnace and kept at 900℃ for 2 hours to obtain silica precursor powder with a moisture content reduced to 5%.

[0048] S7. Airflow milling and classification: The silica precursor powder was milled and classified using an airflow mill. The operating conditions were: milling chamber pressure 0.9 MPa, temperature 35℃, and classifying wheel speed 11000 rpm. Silica micropowder was obtained. The particle size distribution of the silica micropowder is as follows: Figure 5 As shown, the particle size is mainly distributed in the range of 1~5μm, with D10=1.584μm, D50=2.648μm, D90=3.980μm, and the particle size distribution span (D90-D10) / D50=0.90.

[0049] S8. First Surface Modification: The silica micropowder obtained in S7 was put into a high-speed shear mixer, and 3% (by weight) of KH-560 silane coupling agent was added as a modifier. The mixture was reacted at 100℃ and 300 rpm for 2 hours. After the reaction, the mixture was centrifuged and vacuum dried at 90℃ for 2.5 hours to obtain the first-modified silica micropowder.

[0050] S9. Flame Melting and Spheroidizing: The primary modified micro-powder obtained in S8 is continuously fed into a plasma flame melting and spheroidizing furnace for melting and spheroidizing. The working gas is high-purity natural gas and high-purity oxygen, with a volume ratio of 1:2, and the material feed rate is 3 kg / h. The temperature in the spheroidizing zone is controlled at 2000℃, and the material residence time is 1.0 second. After spheroidizing, the particles are rapidly cooled by a water cooling system (cooling water temperature 25℃, flow rate 8 L / min) to obtain spherical coarse silica micro-powder.

[0051] S10. Second surface modification: The spherical silica powder crude product obtained in S9 is put back into the modification equipment and subjected to secondary surface modification using the same modifier (KH-560) and process conditions as in step S8. After the same separation and drying process, the intermediate product is obtained.

[0052] S11. Precise Grading: The intermediate product is graded using an air classifier with a classifying wheel speed of 12,000 rpm. Products within the target particle size range (1~5μm) are collected to obtain the graded product.

[0053] S12. Finished product collection: The graded products are mixed in a closed mixer at 150 rpm for 1 hour. After uniform mixing, the mixture is sealed and packaged to obtain the spherical silicon micro powder finished product.

[0054] Product performance characterization: The spherical silicon micropowder product obtained in Example 1 was tested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that its SiO2 content was ≥99.99%. Scanning electron microscopy (SEM) images of the spherical silicon micropowder product obtained in Example 1 are shown below. Figure 1 As shown, the particle sphericity is approximately 0.97. The particle size distribution of the spherical silica powder obtained in Example 1 was tested using a laser particle size analyzer, and the results are as follows: Figure 9 As shown, the particle size distribution is D10=1.524μm, D50=2.628μm, and D90=4.750μm, indicating good dispersibility and no obvious agglomeration. This demonstrates that the spherical silicon micropowder obtained in Example 1 meets the requirements for fillers in electronic packaging materials.

[0055] Example 2

[0056] In this embodiment, spherical silicon micropowder is prepared using metallic silicon powder as raw material.

[0057] S1. Raw Material Preparation: 80-mesh (approximately 180 μm) metallic silicon powder was used as the raw material. A mixed acid solution of hydrochloric acid and sulfuric acid (volume ratio of hydrochloric acid to sulfuric acid was 2:1, mixed acid concentration was 1.5 mol / L) was added at a volume-to-mass ratio of 6:1 (mL:g). The mixture was stirred at 80℃ for 3 hours. After the reaction was complete, the solution was preliminarily purified by filtration, ultrafiltration (membrane pore size 0.15 μm), and reverse osmosis. Metal ions were then removed by passing the solution through an ion exchange resin column to obtain a high-purity silicic acid solution. This high-purity silicic acid solution had a concentration of approximately 8 wt%, a pH of 4.0, and a conductivity of 25 μS / cm.

[0058] S2. Freezing treatment: The high-purity silica solution obtained in S1 is sent to a solidification device and kept at a constant temperature of -25℃ (temperature fluctuation ±1℃) for 5 hours to form a uniform solid ice body.

[0059] S3. Thawing treatment: Transfer the solid ice to a liquefaction device and treat it at 35°C for 6 hours to obtain a suspension containing silica precipitate.

[0060] S4. Solid-liquid separation: The suspension containing silica precipitate obtained in S3 is subjected to negative pressure filtration at an operating pressure of -0.06 MPa for 1 hour to obtain a filter cake with a water content of 25%.

[0061] S5. Fluidized bed drying: The filter cake obtained in S4 is placed in a fluidized bed drying device and dried at 200℃ for 2.5 hours to obtain a preliminarily dried powder with a moisture content reduced to 15%.

[0062] S6. High-temperature baking: The preliminarily dried powder obtained in S5 is placed in a baking furnace and kept at 1000℃ for 1.5 hours to obtain silica precursor powder, with the moisture content further reduced to 3%.

[0063] S7. Airflow milling and classification: The silica precursor powder is milled and classified using an airflow mill. Operating conditions are: milling chamber pressure 0.9 MPa, temperature 35℃, and classifying wheel speed 11000 rpm. Silica micropowder is obtained. The particle size distribution of the silica micropowder is as follows: Figure 6 As shown, the particle size is mainly distributed in the range of 5~20μm, D10=4.739μm, D50=8.433μm, D90=14.467μm, and the particle size distribution range (D90-D10) / D50=1.15.

[0064] S8. First Surface Modification: The silica micropowder obtained in S7 was placed into a high-speed shear mixer, and 4% (by mass) of a compound modifier (KH-550 silane coupling agent and NDZ-311 titanate coupling agent mixed at a mass ratio of 1:1) was added. The mixture was reacted at 110℃ and 350 rpm for 2.5 hours. After the reaction was completed, the mixture was centrifuged and dried to obtain the first-modified silica micropowder.

[0065] S9. Flame Melting and Spheroidizing: The modified micro-powder is continuously fed into a plasma flame melting and spheroidizing furnace for melting and spheroidizing. The working gas is high-purity natural gas and high-purity oxygen, with a volume ratio of 1:2.2, and the material feed rate is 3.5 kg / h. The temperature in the spheroidizing zone is controlled at 1900℃, and the material residence time is 1.2 seconds. After spheroidization, the particles are rapidly cooled by a water cooling system (cooling water temperature 28℃, flow rate 9 L / min) to obtain spherical coarse silica micro-powder.

[0066] S10. Second surface modification: The spherical silicon micro powder crude product obtained in S9 is put back into the modification equipment and subjected to secondary surface modification using the same compound modifier and process conditions as in step S8. After the same separation and drying process, the intermediate product is obtained.

[0067] S11. Precise Classification: The intermediate product is classified using an air classifier. By adjusting the classifier wheel speed to 12,000 rpm, the product within the target particle size range (5~20μm) is precisely separated and collected to obtain the classified product.

[0068] S12. Finished product collection: The graded product obtained in S11 is mixed in a closed mixer at a speed of 180 rpm for 50 minutes. After uniform mixing, it is sealed and packaged to obtain the spherical silicon micro powder finished product.

[0069] Product performance characterization: The spherical silicon micropowder product obtained in Example 2 was tested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that its SiO2 content was ≥99.99%. Scanning electron microscopy (SEM) images of the spherical silicon micropowder product obtained in Example 2 are shown below. Figure 2 As shown, the particle sphericity is 0.95. The particle size distribution of the spherical silica powder obtained in Example 2 was tested using a laser particle size analyzer, and the results are as follows. Figure 10 As shown, the particle size distribution is D10 = 4.575 μm, D50 = 10.259 μm, and D90 = 20.120 μm. This indicates that the spherical silica powder obtained in Example 2 has excellent purity and sphericity, making it suitable as a functional filler for high-end coatings, composite materials, and other fields.

[0070] Comparative Example 1

[0071] This comparative example uses only "freezing-thawing" without "high-temperature baking" to directly prepare spherical silicon micropowder.

[0072] S1. Raw material preparation: A 20wt% sodium silicate solution was passed through an ion exchange resin column at a flow rate of 2 m / h for ion exchange (exchange temperature 30℃) to obtain a high-purity silicic acid solution. The solution had a concentration of 5wt%, a pH of 3.0, and a conductivity of 25 μS / cm.

[0073] S2. Freezing treatment: The high-purity silica solution obtained in S1 is sent to a solidification device and kept at a constant temperature of -30℃ (temperature fluctuation ±1℃) for 4 hours to form a uniform solid ice body.

[0074] S3. Thawing treatment: Transfer the solid ice to a liquefaction device and treat it at 45°C for 4 hours to obtain a suspension containing silica precipitate.

[0075] S4. Solid-liquid separation: The suspension containing silica precipitate is subjected to negative pressure filtration at an operating pressure of -0.04 MPa for 1 hour to obtain a filter cake with a water content of 20%.

[0076] S5. Fluidized bed drying: Place the filter cake in a fluidized bed drying device and dry it at 180°C for 3 hours to obtain a preliminarily dried powder with a moisture content of 20%.

[0077] S6. Airflow milling and classification: The preliminarily dried powder obtained in S5 is milled and classified using an airflow mill. Operating conditions are: milling chamber pressure 0.9 MPa, temperature 35℃, and classifying wheel speed 11000 rpm. Silica micropowder is obtained. The particle size distribution of the silica micropowder is as follows: Figure 7 As shown, the particle size is mainly distributed in the range of 1~5μm, D10=1.572μm, D50=3.100μm, D90=11.72μm, and the particle size distribution range is (D90-D10) / D50=4.3.

[0078] S7. First Surface Modification: The silica micropowder obtained in S6 was put into a high-speed shear mixer, and 3% (by weight) of KH-560 silane coupling agent was added as a modifier. The mixture was reacted at 100℃ and 300 rpm for 2 hours. After the reaction, the mixture was centrifuged and vacuum dried at 90℃ for 2.5 hours to obtain the first-modified silica micropowder.

[0079] S8. Flame Melting and Spheroidizing: The modified micro-powder is continuously fed into a plasma flame melting and spheroidizing furnace for melting and spheroidizing. The working gas is high-purity natural gas and high-purity oxygen, with a volume ratio of 1:2. The material feed rate is 3 kg / h. The temperature in the spheroidizing zone is controlled at 2000℃, and the material residence time is 1.0 second. After spheroidizing, the particles are rapidly cooled by a water cooling system (cooling water temperature 25℃, flow rate 8 L / min) to obtain spherical coarse silica micro-powder.

[0080] S9. Second surface modification: The spherical silica powder crude product is put back into the modification equipment and subjected to secondary surface modification using the same modifier (KH-560) and process conditions as in step S7. After the same separation and drying process, the intermediate product is obtained.

[0081] S10. Precise Grading: The intermediate product is graded using an air classifier with a classifying wheel speed of 12,000 rpm. Products within the target particle size range (1~5μm) are collected to obtain the graded product.

[0082] S11. Finished product collection: The graded products are mixed in a closed mixer at 150 rpm for 1 hour. After uniform mixing, the mixture is sealed and packaged to obtain the spherical silicon micro powder finished product.

[0083] Product performance characterization: The spherical silicon micropowder product obtained in Comparative Example 1 was tested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that its SiO2 content was ≥99.99%. Scanning electron microscopy (SEM) images of the spherical silicon micropowder product obtained in Comparative Example 1 are shown below. Figure 3 As shown, the spherical silicon micropowder product prepared in Comparative Example 1 has a poor sphericity rate, with most exhibiting irregular shapes. The particle size distribution of the spherical silicon micropowder product prepared in Comparative Example 1 was measured using a laser particle size analyzer, and the results are as follows: Figure 11 As shown, the particle size distribution is D10=1.64μm, D50=3.088μm, and D90=15.07μm, with poor dispersibility and obvious agglomeration. This indicates that the spherical silicon micropowder product prepared in Comparative Example 1 does not meet the requirements for fillers in electronic packaging materials.

[0084] Comparative Example 2

[0085] This comparative example demonstrates the preparation of spherical silica powder using conventional spray drying as a pretreatment process.

[0086] S1. A 20wt% sodium silicate solution was passed through an ion exchange resin column at a flow rate of 2 m / h for ion exchange (exchange temperature 30℃) to obtain a high-purity silicic acid solution. The solution had a concentration of 5wt%, a pH of 3.0, and a conductivity of 25 μS / cm.

[0087] S2. Spray drying: The high-purity silica solution obtained in S1 is fed into a centrifugal spray drying tower. The inlet air temperature is set to 250℃, the outlet air temperature to 110℃, and the atomizing disc rotation speed to 20000 rpm. Dry silica powder is obtained.

[0088] S3. Airflow milling and classification: Silica powder is milled and classified using an airflow mill. Operating conditions are: milling chamber pressure 0.9 MPa, temperature 35℃, and classifying wheel speed 11000 rpm. Silica micropowder is obtained. The particle size distribution of the silica micropowder is as follows: Figure 8 As shown, the particle size is mainly distributed in the range of 1~5μm, D10=1.177μm, D50=2.652μm, D90=9.089μm, and the particle size distribution range (D90-D10) / D50=2.98.

[0089] S4. First Surface Modification: The silica micropowder obtained in S3 was put into a high-speed shear mixer, and 3% (by weight) of KH-560 silane coupling agent was added as a modifier. The mixture was reacted at 100℃ and 300 rpm for 2 hours. After the reaction, the mixture was centrifuged and vacuum dried at 90℃ for 2.5 hours to obtain the first-modified silica micropowder.

[0090] S5. Flame Melting and Spheroidizing: The modified micro-powder is continuously fed into a plasma flame melting and spheroidizing furnace for melting and spheroidizing. The working gas is high-purity natural gas and high-purity oxygen, with a volume ratio of 1:2. The material feed rate is 3 kg / h. The temperature in the spheroidizing zone is controlled at 2000℃, and the material residence time is 1.0 second. After spheroidizing, the particles are rapidly cooled by a water cooling system (cooling water temperature 25℃, flow rate 8 L / min) to obtain spherical coarse silica micro-powder.

[0091] S6. Second surface modification: The spherical silica powder crude product is put back into the modification equipment and subjected to secondary surface modification using the same modifier (KH-560) and process conditions as in step S4. After the same separation and drying process, the intermediate product is obtained.

[0092] S7. Precise Grading: The intermediate product is graded using an air classifier with a classifying wheel speed of 12,000 rpm. Products within the target particle size range (1~5μm) are collected to obtain the graded product.

[0093] S8. Finished product collection: The graded products are mixed in a closed mixer at 150 rpm for 1 hour. After uniform mixing, the mixture is sealed and packaged to obtain the spherical silicon micro powder finished product.

[0094] Product performance characterization: The spherical silicon micropowder product obtained in Comparative Example 2 was tested. The SEM image of the spherical silicon micropowder product obtained in Comparative Example 2 is shown below. Figure 4As shown, it exhibits irregular particles and sintered agglomerates. The particle size distribution of the spherical silica powder product prepared in Comparative Example 2 was measured using a laser particle size analyzer, and the results are as follows. Figure 12 As shown, the particle size distribution is D10=1.622μm, D50=3.687μm, and D90=16.128μm, but the particle dispersibility is poor, with obvious hard agglomeration. The product's pelleting rate is less than 90%. The performance of this product does not meet the requirements for fillers in high-end electronic packaging.

[0095] Test Example 1

[0096] This test case examines the effects of "freezing-thawing" and "high-temperature baking" processes on the ICP impurity concentration of spherical silicon micropowder.

[0097] Impurities in the spherical silicon micropowders prepared in Examples 1, 2 and the comparative examples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to evaluate the effects of the "freeze-thaw" and "high-temperature baking" processes on the ICP impurity concentration of the spherical silicon micropowders. The results are shown in Table 1.

[0098] Table 1. Impurity element content analysis of spherical silicon micropowders prepared by different pretreatment processes.

[0099]

[0100] As shown in Table 1, the only difference between the preparation process of Comparative Example 1 and Example 1 is the omission of the "high-temperature baking" step. The content of key impurities such as Na, K, Ca, Li, and Mn in the spherical silica powder prepared in Comparative Example 1 is 5 to tens of times higher than that in Example 1. Specifically, Na increased tenfold from 0.2 ppm to 2.0 ppm; K increased fifteenfold from 0.1 ppm to 1.5 ppm; Li increased from undetectable to 0.8 ppm; and Ca increased tenfold from 0.1 ppm to 1.0 ppm. This indicates that the "freeze-thaw" step is insufficient to achieve 4N-level ultra-high purity, primarily addressing physical agglomeration but having limited effectiveness in removing chemically bound alkali metals and other impurities. The synergy between "freeze-thaw" and "high-temperature baking" is crucial for achieving the final product, especially the core high-purity indicator of "ultra-low alkali metal content." This step, achieving deep impurity removal at high temperatures, has a decisive impact on the high-end application performance of the product.

[0101] The difference in impurities at the ppm level determines whether a product can be used in high-end electronic packaging. Comparative Example 1 shows the Na content in the spherical silicon micropowder. + K +High levels of alkali metal impurities lead to a surge in dielectric loss, a decrease in insulation resistance, and a dramatic increase in leakage current risk, making it impossible to meet the requirements of high-frequency, high-reliability chip packaging. Alkali metal impurities reduce the strength of the SiO2 network, affect the matching of thermal expansion coefficients, and cause electrochemical migration and corrosion during long-term use, significantly shortening device lifespan.

[0102] The conventional spray drying process in Comparative Example 2 exacerbates hard agglomeration and potential equipment wear, resulting in a multiple or even dozens of times increase in the content of key impurities such as Fe, Al, Na, K, and Ca in the product, making it unable to meet the "ultra-low impurity content" requirements of high-end electronic packaging and other applications.

[0103] Both Examples 1 and 2 employ a "high-temperature baking" step in their preparation methods. The difference lies in the raw materials used. The final products—spherical silicon micropowder—prepared by both methods exhibit extremely low impurity content, falling within the same order of magnitude, with all detected elements having a content below 0.3 ppm. This demonstrates that the "freezing-thawing" and "high-temperature baking" synergistic "depolymerization-stabilization" pretreatment method of this invention can stably produce 4N-grade high-purity (SiO2 ≥ 99.99%) spherical silicon micropowder products from different raw materials (sodium silicate, metallic silicon), indicating a wide range of applicability.

[0104] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing spherical silica micropowder, characterized in that, include: A silica precursor solution was treated using a silica precursor pretreatment method to obtain silica precursor powder. The silica precursor powder was then subjected to melt spheroidization treatment to obtain spherical silica micropowder. The silica precursor pretreatment method includes the following steps: S1. Depolymerization treatment: A silica solution with a concentration of 5wt% to 8wt% and a pH value of 3.0 to 4.0 is frozen to form a solid ice body, then thawed and subjected to solid-liquid separation to obtain a silica precursor filter cake. The freezing temperature is -25℃ to -45℃, and the thawing temperature is 35℃ to 45℃. S2. Stabilization treatment: The silica precursor filter cake obtained in step S1 is subjected to a sand-baking treatment at 900℃~1000℃ to obtain silica precursor powder. The melt spheroidizing treatment is flame melt spheroidizing, the temperature of which is 1900℃~2000℃ and the material residence time is 1.0 second~1.2 seconds; before the melt spheroidizing treatment, the process further includes: airflow pulverization and classification of the silica precursor powder to obtain silica micro powder with a particle size of 1μm~20μm.

2. The preparation method according to claim 1, characterized in that, Also includes: The spherical silica powder obtained after melt spheroidization was subjected to air classification to obtain spherical silica powder with a particle size of 1~20μm.

3. The spherical silica powder prepared by the method of claim 2, characterized in that, The spherical silicon micropowder has a SiO2 content of ≥99.99%, a sphericity of ≥0.95, and a particle size of 1~20μm.

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