A method for preparing high-purity silicon monoxide

Abstract

The application discloses a preparation method of high-purity silicon monoxide and belongs to the technical field of inorganic nonmetal material preparation. The method uses high-purity silicon powder as raw material, adopts a mixed coating agent of silicic acid and tetraethyl orthosilicate, realizes efficient preparation of high-purity silicon monoxide through step-by-step regulation processes of acetic acid catalytic gelation and sulfuric acid density regulation, and combines with segmented calcination and post-treatment purification. Through silicon powder surface hydroxylation pretreatment, double silicon source synergistic coating and precise regulation of sol-gel process, the problems of uneven coating layer, uncontrollable density, low product purity and yield in the traditional coating process are solved. The finally prepared silicon monoxide has a yield of greater than or equal to 85%, a purity of greater than or equal to 99.99%, a total content of metal impurities of less than or equal to 50 ppm and a nonmetal impurity content of less than or equal to 50 ppm, and can meet the high-end application requirements in the fields of electronic devices, new energy and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic non-metallic material preparation, and particularly relates to a preparation method of high-purity silicon monoxide, and is especially suitable for the synthesis of high-purity silicon monoxide for electronic grade and new energy fields. BACKGROUND

[0002] Silicon monoxide (SiO) is an important inorganic non-metallic material, and has a wide application in the fields of lithium ion battery negative electrode, high-temperature ceramic, optical coating, etc. due to its unique physical and chemical properties. Especially in the field of high-end electronic devices, high requirements are put forward for the purity (the silicon content is calculated except for oxygen, and needs to be greater than or equal to 99.99%) and yield (the SiO content needs to be greater than or equal to 85%) of silicon monoxide.

[0003] At present, the preparation methods of silicon monoxide mainly include high-temperature reduction method, flame oxidation method and vacuum oxidation method. Among them, the high-temperature reduction method generates silicon monoxide by mixing silicon powder and silicon dioxide and high-temperature reaction, but the method has problems of uneven mass transfer of the reaction system and easy local over-high temperature, and the SiO yield cannot reach more than 85%; the flame oxidation method has high reaction efficiency, but the product purity is low and the metal impurity content is difficult to control; the vacuum oxidation method needs strict vacuum conditions and has high equipment cost, which is not conducive to large-scale production.

[0004] In order to improve the product purity and reaction controllability, the existing technology often adopts a coating process to pretreat the silicon powder to realize controllable oxidation. For example, some processes adopt a single silicon source (such as only silicic acid or only silane coupling agent) for coating, but the single silicon source is difficult to balance the adhesion and density of the coating layer, and uneven coating is easy to occur; another process introduces a coating agent containing metal, which can improve the coating effect, but introduces additional metal impurities, further reducing the product purity.

[0005] In summary, the existing coating-related patents have the following common defects: (1) single coating system: mostly using a single silicon source (such as only silicic acid, only silane coupling agent) or a coating agent containing a metal source, resulting in poor uniformity of the coating layer or introducing impurities; (2) lack of process regulation: lacking precise regulation means for the density of the coating layer, and unable to balance the contradiction between “oxidation efficiency” and “excessive oxidation”; (3) product positioning deviation: most target products are composite materials (such as silicon-carbon and silicon-lithium), and the process is not targeted at “high-purity SiO”, and the purity is generally lower than 98%. Therefore, developing a silicon monoxide preparation method capable of realizing precise regulation of the uniformity and density of the coating layer and simultaneously improving the yield and purity of the product has become a technical problem to be solved in the field. SUMMARY

[0006] The present application aims to overcome the defects of uneven coating, difficult control of density, low yield and purity in the preparation process of silicon monoxide in the prior art, and provide a preparation method of silicon monoxide with controllable process, uniform coating, adjustable density, and high yield and purity.

[0007] The preparation method of high-purity silicon monoxide provided by the present application comprises the following steps:

[0008] Step 1: Silicon powder pretreatment

[0009] The high-purity silicon powder is sequentially subjected to alkali washing with a NaOH aqueous solution, washing with deionized water, and activation with an H2SO4 aqueous solution to obtain silicon powder with a surface hydroxyl group.

[0010] Step 2: Preparation of coating agent

[0011] The silicic acid and tetraethyl orthosilicate are mixed at a mass ratio of 1:3 to 1:5, a mixed solvent with a volume ratio of ethanol to water of 3:1 to 5:1 is added, and stirring is performed for 20 to 40 minutes to obtain a coating agent. The silicic acid provides initial hydroxyl groups to enhance interfacial bonding, and the tetraethyl orthosilicate is used to construct a dense coating network.

[0012] Step 3: Acid-base stepwise regulation of sol-gel coating

[0013] The silicon powder with a surface hydroxyl group in step 1 is added to the coating agent in step 2, 0.1 to 0.5 mol / L of an aqueous acetic acid solution is added, and stirring is performed at 40 to 70°C for 8 to 12 hours (the acetic acid slowly catalyzes the hydrolysis-polycondensation of the tetraethyl orthosilicate and the silicic acid to form a uniform SiO2 coating layer), 0.1 to 0.5 mol / L of an H2SO4 aqueous solution is further added to adjust the pH of the system to 1.5 to 3.5, and stirring is continued for 1 to 2 hours (the sulfuric acid neutralizes the negative charge on the surface of the sol particles to promote crosslinking and improve the density of the coating layer), thereby obtaining a composite gel of silicon coated with SiO2. The SiO2 coating layer in the composite gel has a gradient structure, the inner layer is a porous SiO2 layer (beneficial to the subsequent diffusion of reaction gas), the outer layer is a dense SiO2 layer (to prevent excessive oxidation of the silicon powder), and the thickness of the coating layer is 40 to 120 nm.

[0014] Step 4: Sectional calcination

[0015] The silica-coated silicon composite gel of step 3 is placed in an inert atmosphere with 0.3% to 1.5% oxygen by volume (a small amount of oxygen balances the oxidation efficiency and prevents excessive oxidation), and is first heated at a rate of 3 to 8°C / min to 350 to 450°C, and held for 1.5 to 2.5 hours (low-temperature solidification removes the physical adsorption water of the coating layer, dehydrates the gel, and forms amorphous SiO2 (to avoid high-temperature cracking); then heated at a rate of 3 to 8°C / min to 800 to 1000°C, and held for 2 to 3 hours (high temperature causes the silicon powder to react with the SiO2 of the coating layer: Si + SiO2 → 2SiO), to obtain a crude silicon monoxide product.

[0016] Step 5: post-treatment purification

[0017] The crude silicon monoxide product of step 4 is subjected to ultrasonic acid washing with an aqueous HCl solution, alternating washing with deionized water and anhydrous ethanol, and vacuum drying, to obtain high-purity silicon monoxide; the purity of the high-purity silicon monoxide is 99.99% to 99.999% (4N to 5N grade), with a total mass content of metal impurities ≤50 ppm, a total mass content of non-metal impurities ≤50 ppm, and a uniformity error <5%.

[0018] Further, in the above step 1, the purity of the high-purity silicon powder is 6N to 9N, and the particle size is 0.5 to 10 μm.

[0019] Further, in the above step 1, preferably the mass concentration of the aqueous NaOH solution is 15% to 25%, and the alkali washing conditions are stirring at 50 to 70°C for 20 to 28 hours, with a silicon powder mass loss rate ≤4.8% and a particle size change rate ≤1.2%, and without excessive hydrolysis.

[0020] Further, in the above step 1, preferably the mass concentration of the aqueous H2SO4 solution is 8% to 12%, and the activation time is 1.5 to 2.5 hours.

[0021] Further, in the above step 2, preferably the mass ratio of the silicic acid to the tetraethyl orthosilicate is 1:4, and the volume ratio of the ethanol to the water is 4:1.

[0022] Further, in the above step 3, preferably the surface-hydroxylated silicon powder of step 1 is added to the coating agent of step 2, 0.2 to 0.4 mol / L aqueous acetic acid is added, stirring is performed at 55 to 65°C for 8 to 12 hours, 0.15 to 0.25 mol / L aqueous H2SO4 is then added to adjust the pH of the system to 2 to 3, and stirring is continued for 1 to 2 hours, to obtain a silica-coated silicon composite gel.

[0023] Further, in the above step 3, preferably the mass ratio of the surface-hydroxylated silicon powder to the coating agent is 1:5 to 1:10.

[0024] Further, in the step 4, the silica-silicon composite gel of step 3 is preferably placed in an inert atmosphere, and the inert atmosphere is mixed with 0.8% to 1.2% oxygen by volume, first heated to 400 DEG C at a rate of 5 DEG C per minute, and then heated to 850 to 950 DEG C at a rate of 5 DEG C per minute, and kept for 2.5 to 3 hours, to obtain a silicon monoxide crude product.

[0025] Further, in the step 5, the mass concentration of the HCl aqueous solution is preferably 8% to 12%, and the ultrasonic power is 150 to 250 W, and the ultrasonic acid washing is 2 to 4 times, each time for 10 to 20 minutes.

[0026] Further, in the step 5, the vacuum drying conditions are preferably as follows: vacuum degree ≤-0.09 MPa, temperature 70 to 110 DEG C, and time 3 to 7 hours.

[0027] The present application realizes efficient preparation of silicon monoxide through an integrated process of "silicon powder surface modification-double silicon source coating-acid-base step-by-step regulation-segmented calcination-precise purification". Compared with the prior art, the present application has the following beneficial effects:

[0028] 1. Through the step-by-step regulation process of "silica-orthosilicic acid ethyl ester double silicon source" coating system and "acetic acid catalytic gelation-sulfuric acid density adjustment", the present application realizes uniform and controllable thickness of the coating layer (50 to 100 nm, uniformity error <5%), and the density is increased by about 40% compared with the traditional process, effectively avoiding excessive oxidation or non-oxidation of silicon powder, and finally increasing the yield of silicon monoxide to more than 85% (about 50% to 60% in the traditional process), the purity reaching more than 99.99%, the total content of metal impurities being ≤50 ppm, and the total content of non-metal impurities being ≤50 ppm, meeting the electronic grade standard.

[0029] 2. The present application uses conventional equipment, combines with online monitoring of the gel process through conductivity, has good potential for large-scale amplification, and significantly enhances the interfacial bonding force between silicon powder and coating agent through optimization of the surface hydroxylation pretreatment process of silicon powder, prevents the coating layer from falling off, and makes the obtained silicon monoxide have direct application stability in high-end fields such as lithium ion battery negative electrode materials, high-temperature oxidation-resistant coatings and optical plating.

[0030] 3. The present application uses a silica-orthosilicic acid ethyl ester system without metal impurities, simplifies the process and controls the impurities, builds through independent coating process and gradient coating layer, takes into account the bonding force and density, precisely controls the sol-gel process, solves the problem of uneven coating, realizes directional preparation of high-purity silicon monoxide, and significantly improves the purity, density and yield. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a scanning electron microscope picture of high-purity silicon powder under 2k (left picture) and 5k (right picture) times.

[0032] Figure 2 is the XRD pattern of high-purity silicon powder.

[0033] Figure 3 is the scanning electron microscope image of silicon monoxide prepared in Example 1 at 2k (left) and 5k (right) times.

[0034] Figure 4 is the XRD pattern of silicon monoxide prepared in Example 1. DETAILED DESCRIPTION

[0035] The application will be further described in conjunction with the accompanying drawings and examples, but the scope of protection of the application is not limited to these examples.

[0036] Example 1

[0037] Step 1: Silicon powder pretreatment

[0038] A two-step method of "alkali washing-activation" is used to perform surface hydroxyl treatment on high-purity silicon powder: first, 50g of silicon powder with purity ≥6N and particle size of 1-5μm is immersed in 200mL of 20% mass concentration NaOH aqueous solution, stirred at 60℃ for 24 hours, so that the Si-O-Si bonds on the surface of the silicon powder are broken, and a large number of Si-OH groups are generated; then, the system is washed with deionized water until the pH value is 7, and the residual NaOH is removed; then, the silicon powder is immersed in 150mL of 10% mass concentration H2SO4 aqueous solution, and activated at room temperature for 2 hours, so that the surface hydroxyl group density is further increased to 2.1mmol / m 2 , and the chemical bonding ability with the subsequent coating agent is enhanced. Finally, the surface-hydroxylated silicon powder is obtained.

[0039] Step 2: Preparation of coating agent

[0040] 10g of silicic acid and 40g of tetraethyl orthosilicate are mixed and added to 100mL of mixed solvent with a volume ratio of ethanol to water of 4:1, and stirred for 30 minutes to obtain the coating agent. In this step, silicic acid and tetraethyl orthosilicate are used as dual silicon sources: silicic acid provides the initial silicon source and hydroxyl groups, ensuring rapid bonding of the coating layer to the surface of the silicon powder; tetraethyl orthosilicate and silicic acid form a dense SiO2 network through hydrolysis-polycondensation reaction, improving the stability of the coating layer; ethanol reduces the surface tension of the system, promoting the uniform dispersion of tetraethyl orthosilicate and silicic acid; and water provides conditions for the hydrolysis reaction.

[0041] Step 3: Acid-base stepwise regulation of sol-gel coating

[0042] 20 g surface hydroxylated silicon powder is added to 140 g coating agent, 50 mL 0.3 mol / L aqueous acetic acid is added, and stirring is carried out in a constant temperature water bath at 60°C for 10 hours. Among them, acetic acid as a weak catalyst, slowly controls the hydrolysis-polycondensation rate of tetraethyl orthosilicate, siliconic acid, forms a porous SiO2 layer on the surface of the silicon powder, avoids uneven coating caused by rapid gel formation, and ensures that a uniform SiO2 coating layer is formed on the surface of each silicon powder. After the gel is formed, 20 mL of 0.2 mol / L H2SO4 aqueous solution is added to adjust the pH of the system to 2.5, and stirring is continued for 1.5 hours. Sulfuric acid neutralizes the negative charge on the surface of the sol particles (Zeta potential decreases from -30 mV to -10 mV), reduces the electrostatic repulsion between particles, promotes particle crosslinking, reduces the average pore size of the SiO2 coating layer from 50 nm to below 18 nm, and increases the density by 42%. Finally, a silicon dioxide coated silicon composite gel is obtained. The SiO2 coating layer in the composite gel has a gradient structure, the inner layer is a porous SiO2 layer with a thickness of 15 nm, the outer layer is a dense SiO2 layer with a thickness of 50 nm, the coating layer thickness is 65 nm, and the uniformity error is <5%.

[0043] Step 4: staged calcination

[0044] A two-stage temperature rising system is adopted to realize the coordination of "coating layer solidification-controllable oxidation". Low-temperature solidification stage: the silicon dioxide coated silicon composite gel of step 3 is placed in a nitrogen atmosphere with 1% oxygen by volume, heated to 400°C at a rate of 5°C / min, and held for 2 hours to remove more than 90% of the physically adsorbed water in the coating layer, dehydrate the gel to form an amorphous SiO2 coating layer, and avoid cracking of the coating layer at high temperature; High temperature reaction stage: continue to heat to 900°C at a rate of 5°C / min, and hold for 3 hours. At this time, the silicon powder reacts with SiO2 in the coating layer: Si + SiO2→ 2SiO. At the same time, the oxygen gas doped in the argon promotes the partial oxidation of the silicon powder and avoids the excessive O2 leading to further oxidation of SiO to SiO2. Finally, a silicon monoxide crude product is obtained.

[0045] Step 5: post-treatment purification

[0046] Through "acid washing-alternating washing-vacuum drying", the impurities are removed in a targeted manner. The silicon monoxide crude product of step 4 is washed with 10% HCl aqueous solution for 3 times, each for 15 minutes, the ultrasonic power is 200W, to remove Fe, Al and other metal impurities; Then wash with deionized water and anhydrous ethanol for 3 times each, deionized water to remove soluble salts, and anhydrous ethanol to reduce the surface tension of the product, avoiding the coating layer cracking during drying; Finally, dry at 100°C under a vacuum degree of ≤-0.09 MPa for 5 hours to avoid the secondary oxidation of SiO caused by O2 and H2O in the air, and obtain high-purity silicon monoxide.

[0047] FromFigure 1 It can be obviously observed that the morphology of the raw material silicon powder is spherical with a particle size of less than 1 μm, which shows characteristic diffraction peaks at 2θ of 28.4°, 47.3°, 56.1°, etc. (see Figure 2 ), and the positions and relative intensities of the peaks are consistent with the standard pattern of crystalline silicon (Si). Figure 3 It can be seen that the obtained silicon monoxide particles are irregular polyhedrons with rough surfaces and micrometer / nanometer level pore structures, and the particle size distribution is relatively narrow, with an average particle size of about 1-5 μm. Figure 4 It can be seen that the crystal form of the obtained product is a typical amorphous silicon monoxide, and the side shows that there is no silicon powder residue on the surface. Table 1 shows the impurity contents of the silicon powder raw material and the silicon monoxide product, in which the purity of the silicon powder reaches more than 6N level, the purity of the silicon monoxide is 99.995%, the level reaches 4.5N level, and the total mass content of metal impurities in the obtained silicon monoxide is 18 ppm, the total mass content of non-metal impurities is 32 ppm, and the uniformity error is <5%.

[0048] Table 1 Impurity contents of silicon powder raw material and silicon monoxide product

[0049]

[0050] Example 2

[0051] Step 1: Silicon powder pretreatment

[0052] 30 g of silicon powder with a purity of ≥6N and a particle size of 1-5 μm was immersed in 120 mL of a NaOH aqueous solution with a mass concentration of 15%, stirred at 70°C for 20 hours, then washed with deionized water until the system pH=7, and then immersed in 90 mL of an H2SO4 aqueous solution with a mass concentration of 12%, activated at room temperature for 1.5 hours, to obtain silicon powder with a surface hydroxyl group (hydroxyl group density 1.8 mmol / m 2 ).

[0053] Step 2: Preparation of coating agent

[0054] 6 g of silicic acid and 30 g of tetraethyl orthosilicate were mixed and added to 60 mL of a mixed solvent of ethanol and water with a volume ratio of 3:1, and stirred for 30 minutes to obtain a coating agent.

[0055] Step 3: Acid-base step-by-step regulation of sol-gel coating

[0056] The 12 g of surface hydroxylated silicon powder is added into 60 g of coating agent, 30 mL of 0.3 mol / L aqueous acetic acid is added, and stirring is carried out in a constant-temperature water bath at 60 ℃ for 8 hours. Then, 12 mL of 0.2 mol / L aqueous H2SO4 is added to adjust the pH of the system to 3, and stirring is continued for 2 hours to obtain a silicon dioxide-coated silicon composite gel. The SiO2 coating layer in the composite gel has a gradient structure, the inner layer is a porous SiO2 layer with a thickness of 10 nm, the outer layer is a dense SiO2 layer with a thickness of 35 nm, the coating layer has a thickness of 45 nm, and the uniformity error is less than 5%.

[0057] Step 4: staged calcination

[0058] The silicon dioxide-coated silicon composite gel of step 3 is placed in a nitrogen atmosphere with 0.8% oxygen by volume, and the temperature is raised to 400 ℃ at a rate of 5 ℃ / min, and the temperature is kept for 2 hours. Then, the temperature is continuously raised to 850 ℃ at a rate of 5 ℃ / min, and the temperature is kept for 3 hours to obtain a silicon monoxide crude product.

[0059] Step 5: post-treatment purification

[0060] The silicon monoxide crude product of step 4 is washed with 10% HCl aqueous solution for 3 times, each time for 15 minutes, and the ultrasonic power is 180 W. Then, the product is washed with deionized water and anhydrous ethanol for 3 times alternately, and finally dried at 100 ℃ under a vacuum degree of ≤-0.09 MPa for 5 hours to obtain high-purity silicon monoxide. The purity of the high-purity silicon monoxide is 99.992%, the total mass content of metal impurities is 43 ppm, the total mass content of non-metallic impurities is 37 ppm, and the uniformity error is 3.8%.

[0061] Example 3

[0062] Step 1: silicon powder pretreatment

[0063] 60 g of silicon powder with a purity of ≥6N and a particle size of 1-5 μm is immersed in 240 mL of 25% NaOH aqueous solution, and stirring is carried out at 60 ℃ for 24 hours. Then, the system is washed with deionized water until the pH is 7, and then immersed in 180 mL of 10% H2SO4 aqueous solution, and activated at room temperature for 1.5 hours to obtain surface hydroxylated silicon powder (hydroxyl density 2.2 mmol / m 2 ).

[0064] Step 2: preparation of coating agent

[0065] 12 g of silicic acid and 36 g of tetraethyl orthosilicate are mixed, and added into 120 mL of mixed solvent with a volume ratio of ethanol to water of 3:1, and stirring is carried out for 30 minutes to obtain a coating agent.

[0066] Step 3: sol-gel coating with stepwise acid-base regulation

[0067] The 24 g of surface-hydroxylated silicon powder was added to 168 g of coating agent, 60 mL of 0.3 mol / L aqueous acetic acid was added, and stirring was performed in a constant-temperature water bath at 60°C for 10 hours. Then, 24 mL of 0.15 mol / L aqueous H2SO4 was added to adjust the pH of the system to 2.8, and stirring was continued for 1.5 hours to obtain a silica-coated silicon composite gel. The SiO2 coating layer in the composite gel has a gradient structure, with a 28 nm-thick porous SiO2 layer in the inner layer, a 42 nm-thick dense SiO2 layer in the outer layer, a coating layer thickness of 70 nm, and a uniformity error of <4.8%.

[0068] Step 4: Staged calcination

[0069] The silica-coated silicon composite gel of Step 3 was placed in a nitrogen atmosphere with 1.4% oxygen by volume, and was heated at a rate of 5°C / min to 400°C, held for 2 hours, then heated at a rate of 5°C / min to 950°C, and held for 3 hours to obtain a crude silicon monoxide product.

[0070] Step 5: Post-treatment purification

[0071] The crude silicon monoxide product of Step 4 was washed three times with 10% HCl aqueous solution under ultrasonic conditions for 15 minutes each time at an ultrasonic power of 150 W, then washed three times with deionized water and three times with anhydrous ethanol, and finally dried at 90°C under a vacuum of ≤-0.09 MPa for 5 hours to obtain high-purity silicon monoxide. The high-purity silicon monoxide has a purity of 99.991%, a total mass content of metallic impurities of 45 ppm, a total mass content of non-metallic impurities of 45 ppm, and a uniformity error of 4.5%.

Claims

1. A method for preparing high-purity silicon monoxide, characterized in that: The preparation method includes the following steps: Step 1: Silicon powder pretreatment High-purity silicon powder was successively washed with NaOH aqueous solution, washed with deionized water, and activated with H2SO4 aqueous solution to obtain surface-hydroxylated silicon powder. Step 2: Preparation of coating agent Silicic acid and tetraethyl orthosilicate are mixed at a mass ratio of 1:3 to 1:5, and a mixed solvent of ethanol and water at a volume ratio of 3:1 to 5:1 is added. The mixture is stirred for 20 to 40 minutes to obtain a coating agent. Step 3: Stepwise regulation of acid-base balance in sol-gel coating The surface-hydroxylated silicon powder from step 1 is added to the coating agent from step 2, and a 0.1–0.5 mol / L acetic acid aqueous solution is added. The mixture is stirred at 40–70°C for 8–12 hours. Then, a 0.1–0.5 mol / L H₂SO₄ aqueous solution is added to adjust the pH of the system to 1.5–3.5, and stirring is continued for 1–2 hours to obtain a silica-coated silicon composite gel. The silica coating layer in the composite gel has a gradient structure, with an inner porous SiO₂ layer and an outer dense SiO₂ layer, and the coating layer thickness is 40–120 nm. Step 4: Segmented calcination The silica-coated silica composite gel from step 3 is placed in an inert atmosphere, and oxygen with a volume fraction of 0.3% to 1.5% is added to the inert atmosphere. The temperature is first increased to 350 to 450°C at 3 to 8°C / min and held for 1.5 to 2.5 hours; then the temperature is increased to 800 to 1000°C at 3 to 8°C / min and held for 2 to 3 hours to obtain crude silica product. Step 5: Post-processing purification The crude silica product from step 4 was subjected to ultrasonic acid washing with HCl aqueous solution, alternating washing with deionized water and anhydrous ethanol, and vacuum drying to obtain high-purity silica. The high-purity silica had a purity of 99.99% to 99.999%, wherein the total mass content of metallic impurities was ≤50ppm, the total mass content of non-metallic impurities was ≤50ppm, and the uniformity error was <5%.

2. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 1, the high-purity silicon powder has a purity of 6N to 9N and a particle size of 0.5 to 10 μm.

3. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 1, the mass concentration of the NaOH aqueous solution is 15%–25%, and the alkaline washing conditions are stirring at 50–70°C for 20–28 hours.

4. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 1, the mass concentration of the H2SO4 aqueous solution is 8% to 12%, and the activation time is 1.5 to 2.5 hours.

5. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 2, the mass ratio of silicic acid to tetraethyl orthosilicate is 1:4, and the volume ratio of ethanol to water is 4:

1.

6. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 3, the surface-hydroxylated silicon powder from step 1 is added to the coating agent from step 2, along with a 0.2–0.4 mol / L aqueous acetic acid solution. The mixture is stirred at 55–65°C for 8–12 hours. Then, a 0.15–0.25 mol / L aqueous H2SO4 solution is added to adjust the pH of the system to 2–3. The mixture is stirred for another 1–2 hours to obtain a silica-coated silicon composite gel.

7. The method for preparing high-purity silicon monoxide according to claim 1 or 6, characterized in that: In step 3, the mass ratio of the surface-hydroxylated silicon powder to the coating agent is 1:5 to 1:

10.

8. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 4, the silica-coated silica composite gel from step 3 is placed in an inert atmosphere, and oxygen with a volume fraction of 0.8% to 1.2% is added to the inert atmosphere. The temperature is first raised to 400°C at 5°C / min and held for 2 hours, then raised to 850 to 950°C at 5°C / min and held for 2.5 to 3 hours to obtain the crude silica product.

9. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 5, the mass concentration of the HCl aqueous solution is 8% to 12%, the ultrasonic power is 150 to 250W, and the ultrasonic acid washing is performed 2 to 4 times, each time for 10 to 20 minutes.

10. The method for preparing high-purity silicon monoxide according to claim 1, characterized in that: In step 5, the vacuum drying conditions are: vacuum degree ≤ -0.09MPa, temperature 70~110℃, and time 3~7 hours.

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