A high-purity ultrafine spherical silica powder, its production method and application

Abstract

This invention discloses a high-purity ultrafine spherical silica powder, its production method, and its application, belonging to the technical field of high-value mineral material preparation and high-value utilization of industrial solid waste. The preparation method includes: flotation and acid washing of silica mud to obtain purified silica powder; air jet milling and air jet classification of the purified silica powder to obtain ultrafine silica powder; and feeding the ultrafine silica powder into a plasma reactor in the presence of an oxygen-containing flow, causing simultaneous oxidation and spheroidization to obtain high-purity ultrafine spherical silica powder. The oxygen volume concentration in the oxygen-containing flow is 25-60%; the ratio of the input power of the plasma reactor to the powder feeding rate of the ultrafine silica powder is 15 kWh / kg-50 kWh / kg. Based on the material characteristics of silica mud, this method achieves high-value utilization of silica mud through the synergistic regulation of pretreatment purification, precise particle size control, and energy-coupled spheroidization throughout the entire process, while possessing advantages such as low energy consumption, uniform product particle size, high purity, and good sphericity.

Description

Technical Field

[0001] This invention relates to a high-purity ultrafine spherical silica powder, its production method, and its application, belonging to the technical field of high-value mineral material preparation and high-value utilization of industrial solid waste. Background Technology

[0002] With the rapid development of the photovoltaic and semiconductor industries, the demand for high-purity silicon materials continues to rise. In the silicon wafer production process, diamond wire is typically used to cut silicon ingots, but this process generates a large amount of cutting waste, namely silicon sludge. Silicon sludge is generated in large quantities and has a low utilization rate. Traditional disposal methods are mostly landfilling or simple recycling, resulting in a waste of high-purity silicon resources. Therefore, developing high-value recycling technologies for silicon sludge is of great significance for promoting the sustainable development of the industrial chain and resource recycling.

[0003] Currently, the resource utilization of silica sludge mainly focuses on recovering silicon metal itself. Existing technologies typically use physicochemical methods such as flotation and acid washing to remove cutting fluid, silicon carbide, and metallic impurities from the silica sludge to obtain high-purity recycled silicon powder. However, the main uses of this recycled silicon powder are still limited to casting silicon ingots with relatively low purity requirements, or as an additive in the smelting of silicon alloys, resulting in limited added value.

[0004] This invention builds upon existing technologies for the separation and purification of silica sludge, combined with research on high-temperature reaction principles and the preparation of spherical silica powder, to innovatively develop a technology for preparing high-purity ultrafine spherical silica powder using silica sludge as raw material. While some researchers have explored using recycled silica powder to prepare spherical silica powder, fundamental technical bottlenecks remain. Two-step processes, which separate the oxidation and spheroidization of silica powder (CN107285322A, etc.), are not only cumbersome but also economically unfeasible due to the need for substantial external energy to melt the silica. One-step methods often employ flame oxidation, but the difficulty in precisely matching the temperature and atmosphere in the high-temperature zone of flame oxidation equipment leads to problems such as non-repeated silica powder oxidation and difficulty in utilizing the exothermic reaction. Summary of the Invention

[0005] To address the problems existing in the prior art, one of the objectives of this invention is to provide a method for preparing high-purity ultrafine spherical silica powder using silica mud as raw material with low energy consumption. Based on the material characteristics of silica mud, this method achieves high-value utilization of silica mud through the coordinated regulation of the entire process of pretreatment purification, precise particle size control, and energy-coupled spheroidization. It also has the advantages of low energy consumption, uniform particle size, high purity, good sphericity, and simple process.

[0006] The second objective of this invention is to provide a high-purity ultrafine spherical silicon powder, wherein the sphericity of the spherical silicon powder product is ≥98%, the sphericity is ≥99%, and the SiO2 content is ≥99.95%.

[0007] The third objective of this invention is to provide an application of high-purity, ultrafine spherical silicon powder in the field of electronic packaging, particularly in epoxy molding compounds, copper-clad laminates for integrated circuit packaging, or special ceramic materials.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for producing high-purity ultrafine spherical silicon micropowder, the method comprising:

[0009] (1) The silica mud is subjected to flotation and acid washing to obtain purified silica powder;

[0010] (2) The purified silicon powder is subjected to air jet milling and air jet classification to obtain ultrafine silicon powder;

[0011] (3) In the presence of an oxygen-containing flow, the ultrafine silicon powder is fed into a plasma reactor, so that the ultrafine silicon powder is simultaneously oxidized and spheroidized to obtain high-purity ultrafine spherical silicon powder;

[0012] The oxygen volume concentration in the oxygen-containing flow is 25-60%; the ratio of the input power of the plasma reactor to the powder feeding rate of the ultrafine silicon powder is 15 kWh / kg-50 kWh / kg.

[0013] The technical solution of this invention is achieved through the synergistic effect of deep purification of silica sludge (flotation process effectively separates silicon powder from organic residues such as cutting fluid, while acid leaching specifically removes metallic impurities), particle size control, and energy-coupled spheroidization. Among these, the energy synergistic design of plasma spheroidization utilizing the exothermic reaction of silicon oxidation is key to achieving low-energy production of spherical silicon micropowder. Based on the characteristic that elemental silicon in silica sludge releases a large amount of heat during oxidation, this invention innovatively transforms this exothermic reaction from a process burden that needs to be controlled into a usable internal heat source. By precisely controlling the oxygen concentration (oxygen volume concentration of 25~60%) in the plasma reactor and the matching relationship between the input power and the ultrafine silicon powder feeding rate (15 kWh / kg~50 kWh / kg), the heat of the elemental silicon oxidation reaction is fully utilized to complete the spheroidization process. This allows the heat released by the silicon powder oxidation reaction to effectively compensate for the external energy input required for spheroidization, enabling the heat released by the silicon powder oxidation reaction to provide 15%~40% of the total heat required for spheroidization. The coordinated control of the above-mentioned process parameters of oxygen concentration, input power, and ultrafine silicon powder feeding rate is the core of achieving low-energy spheroidization. The selection of an oxygen concentration range of 25-60% is based on a balance between reaction kinetics and thermodynamics: when the lower limit is below 25%, the oxidation reaction rate slows down significantly, resulting in insufficient heat of reaction released per unit time, making it difficult to effectively compensate for external energy input. Simultaneously, incompletely oxidized silicon nuclei may be encased in a silica shell, forming a sandwich structure, affecting the chemical homogeneity of the final product. When the concentration exceeds 60%, the oxidation reaction becomes too vigorous, with concentrated instantaneous heat release, easily leading to localized overheating of particles and severe evaporation losses, or causing molten particles to collide and adhere to form sintered bodies, reducing product sphericity and yield. At the same time, oxygen utilization efficiency decreases, resulting in waste. Furthermore, a ratio of input power to ultrafine silicon powder feeding rate of 15-50 kWh / kg ensures that, with the heat of oxidation, the system can still provide sufficient basic energy to maintain a stable plasma arc region and particle sphericity. Too low a ratio results in a large number of unsphericized samples, reducing product sphericity and sphericity. When the ratio exceeds 50 kWh / kg, excessive external energy input occurs even when the heat of oxidation is sufficient, resulting in energy waste. Based on the synergy of the above process conditions, the exothermic reaction of oxidation can efficiently replace 15% to 40% of the external energy input, significantly reducing energy costs. Simultaneously, the uniform release of the reaction heat helps obtain products with more consistent sphericity. This proactive energy regulation strategy overcomes the technical limitations of traditional spheroidization processes that rely solely on external heating and the difficulty in controlling the spherical shape of silicon micropowder prepared from silica mud.

[0014] As a preferred embodiment, the purified silica powder has a purity of ≥99.99%. The purification of the silica sludge lays the purity foundation for subsequent spheroidization.

[0015] It should be noted that the present invention does not have special requirements for the flotation and acid washing purification process, and can use those known in the art. It is only necessary to ensure that the purity of the purified silicon powder obtained after flotation and acid washing is ≥99.99%, so as to provide a raw material basis for the subsequent preparation of high-purity ultrafine spherical silicon powder.

[0016] As a preferred embodiment, the D of the ultrafine silicon powder 50 The particle size distribution is 1~5μm, and the particle size distribution is (D 90 -D 10 ) / D 50 The purity of the ultrafine silicon powder is ≥99.95%, ≤1.0. If the silicon powder particle size is too large, the high heat capacity of the particles during the spheroidization process makes it difficult to achieve uniform spheroidization within a limited temperature and residence time, resulting in poor spheroidization rate and sphericity of the product. This also leads to increased energy consumption and accelerated equipment wear. Conversely, excessively large particle size distribution severely affects the uniformity of the spheroidization process. Different sizes of particles exhibit different behaviors in the same temperature and airflow field; small particles quickly overmelt or agglomerate, while large particles are not fully spheroidized, resulting in uneven sphericity and density of the product, reducing batch stability and overall product performance.

[0017] It should be noted that the combined process of air jet milling and air jet classification in this invention can be achieved by optimizing the coordination between the grinding chamber pressure and the classifier rotation speed. This invention does not have special requirements for specific process flow and parameter conditions; it only needs to obtain the silicon powder particle size D through this process. 50 The particle size distribution is 1~5μm and the particle size distribution (D 90 -D 10 ) / D 50 Ultrafine silica powder with a particle size ≤1.0 is sufficient. Furthermore, the purity of the ultrafine powder obtained by air jet milling and air jet classification is ≥99.95%, which creates favorable conditions for subsequent uniform spheroidization.

[0018] As a preferred embodiment, the oxygen-containing flow is a mixture of inert gas and oxygen.

[0019] As a preferred embodiment, the inert gas is argon and / or nitrogen.

[0020] As a preferred embodiment, the spheroidization temperature is 1600~3000℃, and the material residence time is 0.3~5s. This preferred setting ensures complete spheroidization of the silicon powder while avoiding particle adhesion and heat waste caused by excessively high temperatures. The temperature range directly affects the phase change behavior of the material. By coupling the exothermic oxidation of silicon powder, efficient spheroidization of particles can be achieved at 1600℃. Further lowering the temperature will result in unspheroidized or incompletely spheroidized particles due to insufficient energy, affecting product quality. At temperatures exceeding 3000℃, the material described in this invention can still be efficiently spheroidized, but energy utilization efficiency decreases, a large amount of external heat is not utilized, affecting production energy consumption. Simultaneously, particle adhesion occurs frequently at high temperatures, and some particles deposit on the inner wall of the reactor. The determination of the residence time of 0.3~5s is based on calculations and experimental verification of heat transfer and softening kinetics. A residence time of 0.3s is the minimum time required for this method to ensure that submicron-sized silicon powder undergoes oxidation, melting, and completes spherical reconstruction. If the residence time is too short, incomplete spheroidization will occur, resulting in sharp edges on the particle surface. If the residence time exceeds 5s, problems such as excessive evaporation, collision, and adhesion of molten particles due to prolonged residence in the high-temperature zone will occur.

[0021] As a more preferred embodiment, the spheroidizing temperature is 1600~2000℃, and the material residence time is 0.3~5s. Under this preferred condition, the technology ensures low energy consumption in the process while guaranteeing a high spheroidization rate and high sphericity of the product.

[0022] As a preferred embodiment, the plasma reactor is selected from one of a DC arc plasma furnace, a radio frequency induction plasma furnace, and a microwave plasma furnace.

[0023] As a preferred embodiment, the high-purity ultrafine spherical silicon powder has a sphericity ≥98%, a sphericity ≥99%, a SiO2 content ≥99.95%, and a particle size D. 50 The particle size is 1~5μm, and the particle size distribution (D) 90 -D 10 ) / D 50 ≤1.0. This high-purity ultrafine spherical silicon micropowder can meet the application requirements of high-end electronic packaging materials. Based on the fine grinding and classification process of this invention, the above-mentioned particle size products can be controllably prepared, while the particle size D 50With a particle size of 1~5μm and a narrow distribution, the powder ensures good dispersibility, avoiding the sharp increase in viscosity of subsequent resin slurries caused by excessively fine powder with a large specific surface area. It also fully fills the micro-gaps in integrated circuits, achieving high packing density and a low coefficient of thermal expansion. Excessively fine particles can cause agglomeration, leading to dispersion difficulties and affecting subsequent applications; excessively coarse particles or uneven particle size distribution result in decreased packaging performance. A sphericity ≥98%, sphericity ≥99%, and silica purity ≥99.95% are achieved. This is based on the synergistic control of the raw material and processing ends, particularly the precise regulation of plasma sphericity and the exothermic oxidation of silicon powder. Furthermore, from the product application perspective, advanced packaging places higher demands on material flowability and reliability. High sphericity powder exhibits low resistance in resin, high filling rate, and low curing internal stress, significantly improving device performance and lifespan. Insufficient sphericity leads to stress concentration points from irregular particles, posing a potential risk of device failure. Simultaneously, a product purity ≥99.95% ensures low and controllable impurity content, avoiding impacts on the electrical performance and long-term reliability of integrated circuits.

[0024] A second aspect of the present invention is to provide high-purity ultrafine spherical silicon powder produced by the method described in the first aspect above.

[0025] A third aspect of the present invention is to provide the application of the high-purity ultrafine spherical silicon powder described in the second aspect above in the field of electronic packaging.

[0026] As a preferred embodiment, the high-purity ultrafine spherical silicon powder is used in epoxy molding compounds, copper-clad laminates for integrated circuit packaging, or special ceramic materials.

[0027] In this invention, specific power refers to the ratio of the input power of the plasma reactor to the powder feeding rate of the ultrafine silicon powder.

[0028] Compared with the prior art, the present invention has at least the following advantages:

[0029] (1) Based on the material characteristics of elemental silicon in silica mud, this invention innovatively proposes an energy regulation strategy for efficient utilization of oxidation exothermic process in spheroidization. By synergistically controlling oxygen concentration, plasma power and powder feeding rate, the energy consumption of spheroidization process is significantly reduced, which is 15-40% lower than that of traditional silica spheroidization process.

[0030] (2) The product of the present invention has excellent properties such as high purity, fine particle size, narrow distribution and high sphericity, and is suitable for high-end electronic packaging field.

[0031] (3) This invention transforms silica mud into high-value-added functional powder materials, which not only solves the problem of solid waste disposal in the photovoltaic industry, but also opens up a low-cost raw material channel for the production of spherical silica powder, thus achieving a dual improvement in resource recycling and economic benefits.

[0032] (4) The present invention adopts a one-step process, which efficiently couples the silicon powder oxidation and spheroidization processes to achieve efficient and low-consumption spheroidization. Unlike CN107285322A and others, which separate oxidation and spheroidization, this invention has the advantages of simple process flow, precise parameter control and low energy consumption.

[0033] (5) The process unit equipment used in this invention is mature and reliable, and has the potential for large-scale industrial application, providing a practical and feasible technical path for the high-value utilization of silica mud. Attached Figure Description

[0034] Figure 1 The image shows the morphology of the high-purity ultrafine spherical silicon powder product prepared in Example 1. As can be seen from the image, the particles are uniform in size, nearly perfectly spherical, and no agglomeration or other phenomena were observed. Detailed Implementation

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0038] Example 1

[0039] Silica sludge with a silicon content of 95% was slurried, pH adjusted to 5, and kerosene was added for flotation (kerosene dosage: 150 g / t). The separated silica powder was then acid-washed with hydrochloric acid at a concentration of 15 wt%, a silica powder / acid mass ratio of 1:3, a temperature of 40℃, and a time of 1 hour to obtain high-purity silica powder with a purity of 99.992%. After being pulverized and classified by an air jet mill (inlet pressure: 0.9 MPa, rotation speed: 5000 rpm, feed rate: 10 kg / h), silica powder with a purity of 99.97% and D... 50 =2.5μm, (D 90 -D 10 ) / D 50Ultrafine silicon powder with a particle size of 0.85 was fed into a DC arc plasma furnace. The working gas was an Ar / O2 mixture, with O2 comprising 40% by volume. The specific power was 30 kWh / kg. The reaction zone temperature was approximately 1800℃, and the residence time was approximately 0.8 s. The resulting product, after analysis, had a particle size D... 50 =2.5μm, (D 90 -D 10 ) / D 50 =0.85, sphericity 99.2%, sphericity 98.7%, SiO2 purity 99.97%.

[0040] Example 2

[0041] Silica sludge with a silicon content of 95% was slurried, the pH was adjusted to 4.5, and diesel fuel was added for flotation (200 g / t). The separated silica powder was then acid-washed with sulfuric acid at a concentration of 15%, a silica powder / acid mass ratio of 1:4, a temperature of 30℃, and a time of 0.5 h to obtain high-purity silica powder with a purity of 99.991%. After being pulverized and classified by an air jet mill (inlet pressure 1.0 MPa, rotation speed 5000 rpm, feed rate 20 kg / h), silica powder with a purity of 99.98% and D... 50 =3.0μm, (D 90 -D 10 ) / D 50 Ultrafine silicon powder with a particle size of 1.0 was fed into a DC arc plasma furnace. The working gas was an Ar / O2 mixture, with an O2 volume content of 25%, a specific power of 50 kWh / kg, a reaction zone temperature of approximately 2500℃, and a residence time of approximately 0.3 s. The resulting product, after analysis, had a particle size D... 50 =2.9μm, (D 90 -D 10 ) / D 50 =1.0, sphericity 99.4%, sphericity 98.5%, SiO2 purity 99.99%.

[0042] Example 3

[0043] Silica sludge with a silicon content of 96% was slurried, pH adjusted to 4.5, and diesel fuel was added for flotation (100 g / t). The separated silica powder was then acid-washed with nitric acid at a concentration of 10%, a silica powder / acid mass ratio of 1:3, a temperature of 30℃, and a time of 1.5 h to obtain high-purity silica powder with a purity of 99.994%. This was then further pulverized and classified by an air jet mill (inlet pressure 1.2 MPa, rotation speed 7000 rpm, feed rate 15 kg / h) to obtain silica powder with a purity of 99.99% and D... 50 =1.0μm, (D 90 -D 10 ) / D 50Ultrafine silicon powder with a particle size of 0.8 was fed into a radio frequency induction plasma furnace. The working gas was an Ar / O2 mixture, with O2 comprising 50% by volume. The specific power was 15 kWh / kg. The reaction zone temperature was approximately 1600℃, and the residence time was approximately 5 seconds. The resulting product, after analysis, had a particle size D... 50 =1.0μm, (D 90 -D 10 ) / D 50 =0.77, sphericity 99.3%, sphericity 98.3%, SiO2 purity 99.99%.

[0044] Example 4

[0045] Silica mud with a silicon content of 91% was slurried, the pH was adjusted to 4.8, and kerosene was added for flotation. Diesel fuel was used at a rate of 140 g / t. The separated silica powder was then acid-washed with sulfuric acid at a concentration of 20%, a silica powder / acid mass ratio of 1:3, a temperature of 45℃, and a time of 1 hour, yielding high-purity silica powder with a purity of 99.993%. This was then pulverized and classified by an air jet mill with an inlet pressure of 0.8 MPa, a rotation speed of 6000 rpm, and a feed rate of 30 kg / h, yielding silica powder with a purity of 99.96% and a D... 50 =5.0μm, (D 90 -D 10 ) / D 50 Ultrafine silicon powder with a particle size of 0.9 was fed into a microwave plasma furnace. The working gas was an Ar / O2 mixture, with O2 comprising 60% by volume. The specific power was 22 kWh / kg. The reaction zone temperature was approximately 3000℃, and the residence time was approximately 0.7 s. The resulting product, after analysis, had a particle size D... 50 =4.9μm, (D 90 -D 10 ) / D 50 =0.89, sphericity 99.6%, sphericity 98.4%, SiO2 purity 99.95%.

[0046] Example 5

[0047] The only difference between this comparative example and Example 3 is the ultrafine powder D. 50 =8.0μm, (D 90 -D 10 ) / D 50 =1.5, and the remaining steps and conditions are the same.

[0048] The obtained product, after analysis, has a particle size D. 50 =8.0μm, (D 90 -D 10 ) / D 50 =1.48, sphericity 91%, sphericity 92%, SiO2 purity 99.99%.

[0049] Comparative Example 1

[0050] The only difference between this comparative example and Example 1 is that the volume content of O2 is 15%, while the other steps and conditions are the same.

[0051] The obtained product, after analysis, has a particle size D. 50 =2.5μm, (D 90 -D 10 ) / D 50 =0.82, sphericity 93%, sphericity 87%, SiO2 purity 99.96%.

[0052] Comparative Example 2

[0053] The only difference between this comparative example and Example 1 is the specific power of 10 kWh / kg; all other steps and conditions are the same.

[0054] The obtained product, after analysis, has a particle size D. 50 =2.5μm, (D 90 -D 10 ) / D 50 =0.83, sphericity 90%, sphericity 81%, SiO2 purity 99.96%.

[0055] The results above show that the solution of the present invention can obtain spherical silicon micropowder with high purity, fine particle size, narrow distribution and high sphericity. In Comparative Example 1, the oxygen content is too low, resulting in insufficient heat of reaction released per unit time, which is difficult to effectively compensate for external energy input. At the same time, the incompletely oxidized silicon core is wrapped by the silicon dioxide shell, forming a sandwich structure, thereby reducing sphericity and spheroidization rate. In contrast, the specific power of Comparative Example 2 is too low, and the energy provided by the system cannot maintain a stable plasma arc region and particle spheroidization, thus reducing the spheroidization rate and sphericity of the product.

[0056] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing high-purity ultrafine spherical silica powder, characterized in that: The method includes: (1) The silica mud is subjected to flotation and acid washing to obtain purified silica powder; (2) The purified silicon powder is subjected to air jet milling and air jet classification to obtain ultrafine silicon powder; (3) In the presence of an oxygen-containing flow, the ultrafine silicon powder is fed into a plasma reactor, so that the ultrafine silicon powder is simultaneously oxidized and spheroidized to obtain high-purity ultrafine spherical silicon powder; The oxygen volume concentration in the oxygen-containing flow is 25-60%; the ratio of the input power of the plasma reactor to the powder feeding rate of the ultrafine silicon powder is 15 kWh / kg-50 kWh / kg. The D of the ultrafine silicon powder 50 The particle size distribution is 1~5μm, and the particle size distribution is (D 90 -D 10 ) / D 50 ≤1.0; The spheroidizing temperature is 1600~3000℃, and the material residence time is 0.3~5s.

2. The method for producing high-purity ultrafine spherical silica powder according to claim 1, characterized in that: The purity of the ultrafine silicon powder is ≥99.95%.

3. A method for producing high-purity ultrafine spherical silica powder according to claim 1 or 2, characterized in that: The purified silicon powder has a purity of ≥99.99%.

4. A method for producing high-purity ultrafine spherical silica powder according to claim 1 or 2, characterized in that: The oxygen-containing gas stream is a mixture of inert gas and oxygen.

5. A method for producing high-purity ultrafine spherical silica powder according to claim 1 or 2, characterized in that: The plasma reactor is selected from one of the following: DC arc plasma furnace, radio frequency induction plasma furnace, and microwave plasma furnace.

6. A method for producing high-purity ultrafine spherical silica powder according to claim 1 or 2, characterized in that: The high-purity ultrafine spherical silicon powder has a sphericity ≥98%, sphericity ≥99%, SiO2 content ≥99.95%, and particle size D. 50 The particle size is 1~5μm, and the particle size distribution (D) 90 -D 10 ) / D 50 ≤1.

0.

7. The high-purity ultrafine spherical silica powder produced by the method according to any one of claims 1 to 6.

8. The application of the high-purity ultrafine spherical silicon powder according to claim 7 in the field of electronic packaging.

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