Silica sol, its preparation method and application

Abstract

The application discloses a preparation method of a silica sol, and belongs to the technical field of silica sol preparation. The preparation method comprises the following steps: cleaning and impurity-removing of elemental silicon powder by using dilute acid, separation, and washing of residual acid on the surface of the silicon powder by using water; placing the pretreated silicon powder into a reaction kettle containing water, adding a catalyst and a recyclable solid defoaming agent under stirring, and heating to perform a reaction to obtain a silica sol primary product; standing the silica sol primary product, and recycling the defoaming agent; filtering the silica sol solution to remove unreacted silicon powder; removing alkali metal ions in the silica sol by using an ion exchange resin; and obtaining the silica sol through ultrafiltration. The application further discloses the silica sol prepared by the above preparation method and application. In the silica sol reaction process, the recyclable solid defoaming agent is added, the problem of floating of the elemental silicon powder in the reaction is significantly improved, the reaction efficiency and yield are improved, the influence of the defoaming agent on the purity of the silica sol is avoided, the production cost is reduced, and the production process is simple, the production cycle is short, and the efficiency is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silica sol preparation, in particular to a silica sol and a preparation method and application thereof. BACKGROUND

[0002] Silica sol is a translucent liquid with milky white or white color, and the colloidal particles are approximately spherical. The concentration of silicon dioxide is generally 10-40%, the particle size is 5-100 nm, and most of them are stable alkaline, and a small number of them are acidic.

[0003] Silica sol has good corrosion resistance, insulation, adsorption, large specific surface area and other physicochemical properties, and has the advantages of wide raw material sources, easy operation, no harm to the environment and human beings, and is widely used in chemical industry, material industry, textile / papermaking industry, electronic industry and other fields.

[0004] In low-end applications, silica sol is used as a binder for precision casting shell instead of ethyl silicate and water glass which are harmful to the environment; the mixture of silica sol and photosensitive liquid is used to treat photosensitive paper, which can make the surface of the photosensitive paper smooth and the image more clear; the mixture of silica sol and organic polymer emulsion has the advantages of strong film forming rigidity, pollution resistance, strong dust resistance, and composition not easy to volatilize.

[0005] In medium and high-end applications, silica sol can be used as a catalyst carrier, such as a three-way catalyst for automobile exhaust treatment, a catalyst for flue gas denitrification in power plants and acrylonitrile synthesis in the petrochemical field, which can improve the reaction activity and selectivity of the catalyst; silica sol is also used for chip wafer polishing, and has the advantages of moderate hardness, long-term stable storage, less scratches during CMP, and easy cleaning.

[0006] At present, most of the domestic medium and high-end silica sols are dependent on imports, and the long-term stability of low metal ion high concentration has not reached the standard of foreign countries, especially in the important fields of chip polishing and catalyst carrier, which has been in a state of neck. Since these industries are currently in a period of development and prosperity, the scale and market are also expanding, and the demand and requirements for silica sol are also increasing. As a green material, silica sol will undoubtedly receive the most widespread attention in the future development, because it is a non-toxic substance and has very low pollution.

[0007] The main preparation methods of silica sol at present include ion exchange method, elemental silicon hydrolysis method, electrolytic electrodialysis method, peptization method and silicate hydrolysis method, but the silica sol applied in industry is mainly prepared by ion exchange method and elemental silicon hydrolysis method. In the ion exchange method, the raw material for preparing silica sol is water glass, and the quality factors of water glass have a direct impact on the production of silica sol. The water glass with high impurity content is not conducive to the preparation of silica sol. The one-step dissolution method of elemental silicon uses industrial pure silicon as raw material, and the process for preparing silica sol from silicon powder is simple, the cost is low, the particle shape and particle size of silicon dioxide are easy to control, and the stability of colloidal particles is good. However, the silica sol prepared from silicon powder still has problems of low product concentration and low yield.

[0008] A large amount of hydrogen gas is generated in the process of generating silica sol from silicon powder under the action of catalyst. According to calculation, 1 kg of pure silicon powder generates 399.6 L of hydrogen gas to generate silica sol, thereby generating a large amount of bubbles on the surface of silicon powder. During the reaction process, the silicon powder inevitably floats and aggregates to form foam, which hinders the contact between silicon powder and reaction liquid, resulting in a decrease in reaction efficiency and yield.

[0009] The silica sol for synthesizing acrylonitrile catalyst and the preparation method thereof are disclosed in Chinese patent document CN 110562990 A. By adding a certain concentration of stabilizers such as Nianale and polyvinyl alcohol into the reaction liquid before concentration during the preparation process, the gelation time of silica sol can be more than 1 year when the concentration of silicon dioxide is more than 40%, which greatly improves the stability of the silica sol.

[0010] The utility model discloses a kind of silica sol preparation reaction kettles, and the silica sol preparation reaction kettle includes reaction kettle and the stirring device horizontally arranged in reaction kettle, the sidewall of the bottom of the reaction kettle is connected with material circulation discharge pipe, the end of the material circulation discharge pipe is provided with electric on-off valve for controlling its discharge on-off, the outlet of the material circulation discharge pipe is connected with the feed inlet of circulating pump, and the discharge outlet of the circulating pump is connected with circulation pipeline.The utility model discloses a kind of silica sol preparation reaction kettles, and the silica sol preparation reaction kettle includes reaction kettle and the stirring device horizontally arranged in reaction kettle, the sidewall of the bottom of the reaction kettle is connected with material circulation discharge pipe, the end of the material circulation discharge pipe is provided with electric on-off valve for controlling its discharge on-off, the outlet of the material circulation discharge pipe is connected with the feed inlet of circulating pump, and the discharge outlet of the circulating pump is connected with circulation pipeline.

[0011] The Chinese patent document with the publication number CN 110127704 A discloses an alkaline nano-silicon sol that can reduce silicon powder residue and improve silicon powder utilization. The alkaline nano-silicon sol is obtained by dispersing industrial silicon powder in a deionized water and mixed catalyst dispersion system, coating active silicon acid particles on the surface of nano-silicon dioxide particles as a core. The mixed catalyst is a system composed of multiple alkalis and catalysts, and has high catalytic efficiency. The invention can effectively improve the utilization rate of silicon powder, greatly reduce the problem of silicon powder residue, and the prepared silicon sol has good stability, uniform particle size distribution, etc.

[0012] As can be seen from the above, the prior art has made certain research on the problem of low product concentration and low yield of silicon sol prepared from silicon powder, and some methods to solve this problem have been disclosed. Although these disclosed methods have certain effects, the effects are not obvious. Therefore, it is of great significance to find a simple and easy-to-operate preparation method of silicon sol, greatly improve the reaction efficiency and reaction yield of elemental silicon powder for preparing silicon sol, and reduce the production cost. SUMMARY

[0013] To overcome the problems of low yield and long reaction time of silicon sol prepared from elemental silicon, the present invention provides a preparation method of silicon sol. The method uses elemental silicon as raw material and adds recyclable defoaming agent during preparation, thereby improving reaction efficiency and reaction yield and reducing production cost.

[0014] A preparation method of silicon sol, comprising the following steps:

[0015] (1) Elemental silicon powder pretreatment: the elemental silicon powder is cleaned and impurities are removed by using dilute acid, separated, and the acid remaining on the surface of the silicon powder is washed with water;

[0016] (2) Silicon sol preparation: the pretreated silicon powder is placed in a reaction kettle containing water, and a catalyst and a recyclable solid defoaming agent are added under stirring conditions, and the reaction is carried out by heating to obtain a silicon sol initial product;

[0017] (3) Silicon sol purification: the silicon sol initial product is allowed to stand, and the defoaming agent is recovered; the silicon sol solution is filtered to remove unreacted silicon powder; and ion exchange resin is used to remove alkali metal ions in the silicon sol;

[0018] (4) Silicon sol concentration: silicon sol is obtained by ultrafiltration.

[0019] Preferably, in step (1), the particle size of the elemental silicon powder is 50-500 mesh, and the purity is greater than 95%.

[0020] Preferably, in step (1), the dilute acid is dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid or hydrofluoric acid.

[0021] The present application adopts dilute acid cleaning to remove iron, aluminum, calcium and other impurities in silicon powder, and the concentration and frequency of acid cleaning can be appropriately changed according to the purity of the silicon powder. Since the surface of small particle silicon powder is easy to be oxidized to form a silicon dioxide inert layer, affecting the reaction efficiency, therefore, for small particle silicon powder, hydrofluoric acid washing is appropriately added.

[0022] The type and amount of catalyst has an important influence on the silica sol. Preferably, in step (2), the catalyst is one or more of sodium hydroxide, potassium hydroxide, ammonia or a strong organic base.

[0023] Preferably, the strong organic base includes guanidine compounds.

[0024] In the present application, organic weak base catalysts (such as organic amine) are not used, because such defoaming agents will reduce the reaction yield.

[0025] Preferably, in step (2), the catalyst mass is 0.1-1.0% of the mass of elemental silicon.

[0026] Preferably, in step (2), the recyclable solid defoaming agent is a hydrophobic and water-insoluble defoaming particle, and the particle surface is free of emulsifiers.

[0027] In the present application, a defoaming agent is added to the reaction solution for preparing the silica sol, effectively reducing the interfacial tension between the hydrogen gas bubbles and the reaction solution, allowing the gas bubbles to quickly detach from the surface of the silicon powder, effectively inhibiting the generation of silicon powder foam, increasing the contact area of the silicon powder and the reaction solution, and greatly improving the reaction efficiency and yield. By adding a solid defoaming agent, the reaction time of the silica sol can be shortened to 2-4h, achieving a yield of more than 90%.

[0028] Preferably, in step (2), the defoaming particle has a particle size of 10nm-500mm.

[0029] Preferably, in step (2), the mass of the defoaming agent is 0.1-20% of the mass of elemental silicon.

[0030] Preferably, the defoaming particle includes hydrophobically modified silica, aluminum oxide, calcium carbonate, titanium dioxide and barium sulfate. After the silica sol primary product is left to stand, the solid defoaming agent floats on the surface of the liquid and is recycled.

[0031] Preferably, the defoaming particle is a superparamagnetic particle, coated with silica on the surface, and forms a solid defoaming agent after hydrophobic modification. After the silica sol primary product is left to stand, the solid defoaming agent floats on the surface of the liquid and is recycled by magnetism.

[0032] Preferably, in step (2), the reaction temperature is 80-95℃, and the time is 2-10h.

[0033] Preferably, in step (4), the yield of the silica sol is 90-95%.

[0034] Preferably, in step (4), the particle size of the silica sol is 10-35 nm.

[0035] Preferably, in step (4), the silica content in the silica sol is greater than 30 wt%.

[0036] The present application also provides a silica sol prepared by the above preparation method. The silica sol has high stability, high specific surface area and highly adjustable particle size distribution.

[0037] The present application also provides the use of the above silica sol in chip polishing, catalyst carrier and electronic coating. The silica sol of the present application has good stability, high specific surface area and controllable particle size distribution, and has broad application prospects in the fields of chip polishing, catalyst carrier and electronic coating.

[0038] The silica sol of the present application has high dispersion stability, controllable particle size distribution, acid and alkali resistance and thermal stability, and can be used in chip polishing liquid, greatly improving the polishing efficiency and precision, reducing surface defects and scratches, making the surface smoother and flatter, and widely used in the fields of semiconductor manufacturing, optical devices and precision instruments.

[0039] The silica sol of the present application has high concentration and specific surface area and highly adjustable particle size distribution, and is very suitable for use as a catalyst carrier for different types of catalysts, and can be used in the fields of catalytic chemistry, environmental management, chemical pharmacy, etc.

[0040] The silica sol of the present application can be used in electronic product coating to improve the rheological properties and coating performance of the coating, and increase the electrical insulation and heat resistance of the coating.

[0041] Preferably, when the silica sol is used as a catalyst carrier, in step (2), the reaction time is 2-4 h.

[0042] Compared with the prior art, the present application has the following advantages:

[0043] (1) In the process of preparing the silica sol of the present application, a recyclable defoaming agent is added to solve the problem of elemental silicon powder floating, greatly improving the reaction efficiency and reaction yield of elemental silicon powder. In the present application, by adding a solid defoaming agent, the reaction time is shortened to 2-4 h, and the yield of the silica sol is more than 90%.

[0044] (2) The defoaming agent of the present application is recyclable and easy to recycle. The recycling of the defoaming agent avoids the influence of the defoaming agent on the purity of the silica sol, and at the same time reduces the production cost.

[0045] (3) The catalyst used in the preparation of the silica sol has low content, which reduces the difficulty of subsequent treatment, and has less pollution.

[0046] (4) The present application uses elemental silicon as raw material, has simple production process, short production cycle, high efficiency, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The transmission electron microscope image of the silica sol prepared in Example 1 of the present application.

[0048] Figure 2 The transmission electron microscope image of the silica sol prepared in Example 2 of the present application.

[0049] Figure 3 The transmission electron microscope image of the silica sol prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0050] Example 1

[0051] 500g of elemental silicon powder with a particle size of 50 mesh was pretreated with 10% dilute hydrochloric acid, washed twice, and then washed with deionized water to remove the hydrochloric acid on the surface of the silicon powder. 800mL of deionized water was added to a 10L reaction kettle and stirred, 4g of sodium hydroxide was added to the reaction kettle and stirred to dissolve; the pretreated silicon powder was added to the reaction kettle and stirred uniformly; then 10g of solid defoaming agent hydrophobic silica was slowly added to the reaction kettle and stirred. The temperature was raised to 90℃, and the reaction was carried out for 4h to obtain the initial product of silica sol. The initial product of silica sol was allowed to stand, and the defoaming agent was recovered; the silica sol solution was filtered to remove unreacted silicon powder; and ion exchange resin was used to remove alkali metal ions in the silica sol. The silica sol was concentrated to 30wt% by ultrafiltration method.

[0052] The particle size of the silica sol prepared in this example was 31nm, the solid content was 30wt%, and the yield was 90% (see Table 1), and its transmission electron microscope image is as shown in Figure 1 .

[0053] Example 2

[0054] 500 g of elemental silicon powder with a particle size of 200 mesh was pretreated with 5% dilute nitric acid, washed twice, and after separation, washed with deionized water to remove the nitric acid on the surface of the silicon powder. 800 mL of deionized water was added to a 10 L reaction kettle and stirred, and 5 g of potassium hydroxide was added to the reaction kettle and stirred to dissolve; the pretreated silicon powder was added to the reaction kettle and stirred uniformly; then 20 g of solid defoaming agent hydrophobic alumina was slowly added to the reaction kettle and stirred. The temperature was raised to 90°C, and the reaction was carried out for 3 h to obtain a silicon sol primary product. The silicon sol primary product was allowed to stand, and the defoaming agent was recovered; the silicon sol solution was filtered to remove unreacted silicon powder; and ion exchange resin was used to remove alkali metal ions in the silicon sol. The silicon sol was concentrated to 40 wt% by ultrafiltration.

[0055] The particle size of the silicon sol prepared in this example was 22 nm, the solid content was 40 wt%, and the yield was 92% (see Table 1), and the transmission electron micrograph thereof is shown in FIG. 1. Figure 2

[0056] Example 3

[0057] 500 g of elemental silicon powder with a particle size of 500 mesh was pretreated with 10% dilute hydrochloric acid and 0.5% hydrofluoric acid, washed twice, and after separation, washed with deionized water to remove the hydrochloric acid and hydrofluoric acid on the surface of the silicon powder. 800 mL of deionized water was added to a 10 L reaction kettle and stirred, and 2 g of tetramethyl guanidine was added to the reaction kettle and stirred to dissolve; the pretreated silicon powder was added to the reaction kettle and stirred uniformly; then 50 g of solid defoaming agent hydrophobic silica-coated magnetite was slowly added to the reaction kettle and stirred. The temperature was raised to 95°C, and the reaction was carried out for 2 h to obtain a silicon sol primary product. The silicon sol primary product was allowed to stand, and the defoaming agent was recovered; the silicon sol solution was filtered to remove unreacted silicon powder; and ion exchange resin was used to remove alkali metal ions in the silicon sol. The silicon sol was concentrated to 30 wt% by ultrafiltration.

[0058] The particle size of the silicon sol prepared in this example was 14 nm, the solid content was 30 wt%, and the yield was 95% (see Table 1), and the transmission electron micrograph thereof is shown in FIG. 2. Figure 3

[0059] Comparative Example 1

[0060] 500 g of elemental silicon powder with a particle size of 50 mesh was pretreated with 10% dilute hydrochloric acid, washed twice, and after separation, washed with deionized water to remove the hydrochloric acid on the surface of the silicon powder. 800 mL of deionized water was added to a 10 L reaction kettle and stirred, and 4 g of sodium hydroxide was added to the reaction kettle and stirred to dissolve; the pretreated silicon powder was added to the reaction kettle and stirred uniformly. The temperature was raised to 90°C, and the reaction was carried out for 4 h to obtain a silicon sol primary product. The silicon sol solution was filtered to remove unreacted silicon powder; and ion exchange resin was used to remove alkali metal ions in the silicon sol. The silicon sol was concentrated to 30 wt% by ultrafiltration.​​

[0061] The particle size of the silica sol prepared in the present comparative example was 30 nm, the solid content was 30 wt%, and the yield was 50% (see Table 1).

[0062] Comparative Example 2

[0063] 500 g of elemental silicon powder having a particle size of 50 mesh was pretreated with 10% dilute hydrochloric acid, washed twice, and after separation, washed with deionized water to remove the hydrochloric acid on the surface of the silicon powder. 800 mL of deionized water was added to a 10 L reaction kettle and stirred, 4 g of sodium hydroxide was added to the reaction kettle and stirred to dissolve; the pretreated silicon powder was added to the reaction kettle and stirred uniformly; then 10 g of silicone antifoaming agent was slowly added to the reaction kettle and stirred. The temperature was raised to 90°C, and the reaction was carried out for 4 h to obtain a crude silica sol. The crude silica sol was allowed to stand, and the antifoaming agent was recovered; the silica sol solution was filtered to remove unreacted silicon powder; and ion exchange resin was used to remove alkali metal ions in the silica sol. The silica sol was concentrated to 30 wt% by ultrafiltration.

[0064] The particle size of the silica sol prepared in the present comparative example was 28 nm, the solid content was 30 wt%, and the yield was 32% (see Table 1).

[0065] Table 1 Particle size, solid content, and yield of the silica sol prepared in Examples 1-3 and Comparative Examples 1-2

[0066] Sample Particle size Solid content Yield Example 1 31 nm 30 wt% 90％ Example 2 22 nm 40 wt% 92％ Example 3 14 nm 30 wt% 95％ Comparative Example 1 30 nm 30 wt% 50％ Comparative Example 2 28 nm 30 wt% 32％

Claims

1. A method for preparing silica sol, characterized in that, Includes the following steps: (1) Pretreatment of elemental silicon powder: The elemental silicon powder is cleaned and purified with dilute acid, separated, and the acid residue on the surface of the silicon powder is washed with water. (2) Preparation of silica sol: The pretreated silica powder is placed in a reaction vessel containing water, and a catalyst and a recyclable solid defoamer are added under stirring. The reaction is carried out by heating to obtain the initial silica sol product. (3) Silica sol purification: Let the initial silica sol stand and recover the defoamer; filter the silica sol solution to remove unreacted silica powder; remove alkali metal ions from the silica sol using ion exchange resin; (4) Silica sol concentration: Silica sol is obtained by ultrafiltration.

2. The method for preparing silica sol according to claim 1, characterized in that, In step (1), the particle size of the elemental silicon powder is 50-500 mesh and the purity is greater than 95%.

3. The method for preparing silica sol according to claim 1, characterized in that, In step (2), the catalyst is one or more of sodium hydroxide, potassium hydroxide, ammonia, or a strong organic base, and the mass of the catalyst is 0.1 to 1.0% of the mass of elemental silicon.

4. The method for preparing silica sol according to claim 1, characterized in that, In step (2), the recyclable solid defoamer is a hydrophobic and water-insoluble defoaming particle with a particle size of 10 nm to 500 mm and a mass of 0.1 to 20% of the mass of elemental silicon.

5. The method for preparing silica sol according to claim 4, characterized in that, The defoaming particles include hydrophobically modified silica, alumina, calcium carbonate, titanium dioxide, and barium sulfate.

6. The method for preparing silica sol according to claim 4, characterized in that, The defoaming particles are superparamagnetic particles coated with silica, which are then modified by hydrophobicity to form a solid defoamer.

7. The method for preparing silica sol according to claim 1, characterized in that, In step (2), the reaction temperature is 80-95℃ and the time is 2-10h.

8. The method for preparing silica sol according to claim 1, characterized in that, In step (4), the yield of the silica sol is 90-95%, the particle size is 10-35 nm, and the silica content in the silica sol is greater than 30 wt%.

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