A small-particle-size silica sol, its preparation method and application

Abstract

The application provides a small-particle-size silica sol, a preparation method and application thereof, and the preparation method comprises the following steps: stirring and mixing a sodium silicate aqueous solution in a stirring cylinder provided with resin to perform ion exchange, so as to obtain active silicic acid; taking part of the active silicic acid, adding an alkaline substance into the active silicic acid, and making the pH value of the active silicic acid be 8.5-9.5 to perform a first reaction, so as to obtain crystal seeds; and after concentration, the silica sol is obtained; and the speed of adding the sodium silicate aqueous solution into the stirring cylinder is M / 3 min-M / 1 min, and M is the mass of the sodium silicate aqueous solution. The silica sol provided by the technical scheme of the application has small particle size and excellent stability, and can be stored for a long time.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a small-particle-size silica sol, its preparation method, and its applications. Background Technology

[0002] Silica sol is a stable colloidal system formed by uniformly dispersing nano-sized silica particles in water or organic solvents. It is essentially a polymer of silicic acid and has properties such as high specific surface area, good permeability and chemical inertness. It is widely used in precision casting, coatings, catalyst carriers and electronic materials.

[0003] Small-particle-size silica sols specifically refer to products whose primary silica particles typically have a diameter of less than 10 nm. Due to their extremely small size, these sols exhibit unique advantages, such as extremely high specific surface area, excellent film density, superior light transmittance, and better penetration and filling capabilities, making them key materials in cutting-edge fields such as high-performance coatings, CMP abrasives, advanced binders, and functional nanocomposites.

[0004] Small-particle-size silica sols are mainly prepared through ion exchange: diluted water glass (sodium silicate solution) is passed through an ion exchange resin to remove sodium ions, yielding active silicic acid, which is then condensed and grown under controlled conditions to form silica sol; and elemental silicon hydrolysis: elemental silicon powder reacts directly with water under the action of a catalyst to generate silica sol and hydrogen gas, thus preparing small-particle-size silica sols. Both methods face significant stability challenges: ① The synthesis of small-particle-size silica sols using the ion exchange method requires the addition of alcohols, aldehydes, etc., as polymerization inhibitors, which not only increases raw material costs but also necessitates additional processes to remove these inhibitors, increasing process complexity and environmental pressure. ② The elemental silicon method struggles to produce products with narrow particle size distributions, resulting in low product quality. ③ Furthermore, both methods suffer from poor stability, such as easy gelation and agglomeration of the product.

[0005] Therefore, developing a method to effectively control particle size distribution and improve the stability of silica sol remains a key research focus. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a small particle size silica sol, its preparation method and application, to solve the problems in the prior art.

[0007] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0008] The first aspect of this invention provides a method for preparing small-particle-size silica sol, comprising the following steps:

[0009] Sodium silicate aqueous solution is stirred and mixed in a stirring tank containing resin to carry out ion exchange, thereby obtaining active silicic acid;

[0010] Take a portion of active silicic acid, add an alkaline substance to it to make the pH 8.5~9.5 to carry out the first reaction, and obtain seed crystals;

[0011] The silica sol was obtained after concentration;

[0012] The sodium silicate aqueous solution is added to the stirring tank at a rate of M / 3min to M / 1min, where M is the mass of the sodium silicate aqueous solution.

[0013] The pH can be 8.5, 9.0, or 9.5; the addition rate into the mixing tank can be M / 3min~M / 2min, M / 2min~M / 1min, or M / 2.95min~M / 1.2min.

[0014] The active silicic acid in this application is a monomer or oligomer of silicic acid (usually referring to orthosilicic acid, Si(OH)4), which contains a large number of active silanol groups (Si-OH), giving it extremely high chemical reactivity, namely, a strong tendency to polymerize and instability.

[0015] Preferably, the concentration of the sodium silicate aqueous solution is 7.0~12.0 wt%. For example, it can be 8~11 wt% or 7~11 wt%.

[0016] Preferably, the mass ratio of the sodium silicate aqueous solution to the resin is 1:0.8~2. For example, it can be 1:1~2, 1:1~1.5, 1:1, or 1:1.5.

[0017] Preferably, the stirring speed during ion exchange is 150-300 rpm. The stirring speed can be 150 rpm, 200 rpm, 250 rpm, or 300 rpm.

[0018] Preferably, the resin is a strong acid cation exchange resin. Specifically, it can effectively exchange cations regardless of the pH value of the exchange system solution (even under strongly acidic conditions).

[0019] Preferably, the total exchange capacity of the resin, based on a dry basis, is ≥4.0 mmol / g. Specifically, the total exchange capacity of the resin refers to the capacity per gram of resin to exchange cations being greater than or equal to 4.0 mmol, theoretically capable of exchanging all cations in a solution; in this application, it mainly refers to sodium ions in a sodium silicate solution.

[0020] Preferably, the resin is selected from one or more of 001×7, 001×8, D001, Tulsimer® T-42 H, and Amberlyst 15.

[0021] Specifically, the resin is activated before use to give it good ion exchange capacity. This application does not specify the activation method; the standard activation process for the corresponding resin in the prior art is sufficient.

[0022] Preferably, the ion exchange reaction time is 0.5 to 1 hour. For example, it can be 0.6 hours, 0.7 hours, 0.8 hours, or 0.9 hours.

[0023] Preferably, the concentration of the active silicic acid is 2.0~5.0 wt%. For example, it can be 3 wt%, 4 wt%, or 4.5 wt%.

[0024] The method for preparing active silicic acid in this application differs from the commonly used ion-column exchange method in the prior art (where sodium silicate aqueous solution is added to one end of the ion-column and active silicic acid is collected at the other end). This technical solution provides a specific method for preparing active silicic acid by controlling the amount of resin and the rate at which the sodium silicate aqueous solution is added to the stirring tank (the flow rate when in contact with the resin), combined with stirring and other technical features, thereby resulting in more active silicic acid with better activity, providing a good foundation for the preparation of highly stable silica sol. The technical effect of this application can only be achieved within the range of addition rate and resin amount specified in this application.

[0025] Preferably, the alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, isopropylamine, dimethylenetriamine, and 2-amino-2-methyl-1-propanol (AMP).

[0026] The alkaline substance selected in this application can be chosen based on the requirements for metal impurities in the final product. For example, if the requirements for the content of metal impurities in the final product silica sol are strict, ammonia or AMP can be selected to avoid introducing additional impurities.

[0027] Preferably, the concentration of the alkaline substance is 5-30 wt%. For example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, or 25 wt%.

[0028] Preferably, when adding the alkaline substance and carrying out the first reaction, stirring is performed at a speed of 100-300 rpm. For example, the stirring speed can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, or 300 rpm.

[0029] Preferably, the temperature of the first reaction is 95~105℃, and the time of the first reaction is 20~50min. The temperature can be 98~100℃ or 98~102℃; the time can be 24~36min, 20~36min, or 24~50min.

[0030] Preferably, the seed crystal has a particle size of 3-5 nm. For example, it can be 3-4 nm or 4-5 nm.

[0031] Preferably, after obtaining the seed crystal, the process further includes adding active silicic acid dropwise to the seed crystal to carry out a second reaction, followed by concentration after the second reaction is completed. By adding active silicic acid dropwise to the seed crystal a second time, the particle size of the final silica sol can be adjusted to increase the particle size range of the silica sol and meet different application directions in actual production.

[0032] Preferably, during the second reaction, the alkaline substance is continuously added so that the pH of the reaction system is 9.5 to 10.5.

[0033] The pH of the system during the second reaction in this application affects the performance of the product. Only by reacting within this pH range can small-particle-size, highly stable silica sol be obtained. If the pH is too low, such as 9.0, the dissociation rate of active silicic acid will decrease, the condensation reaction will slow down, resulting in uneven crystal nuclei size, affecting the uniformity of the product. Furthermore, low pH will result in insufficient negative charge on the surface of silica sol particles, weakening the repulsive force and making them prone to aggregation. If the pH is too high, such as 11, the condensation reaction rate will be too fast, nucleation and growth will be out of control, the particle size distribution will widen, and the particle growth tendency will be enhanced, making it difficult to obtain small-particle-size products. In addition, excessive alkali will introduce more metal ions, reducing the purity of the product.

[0034] Preferably, in the second reaction, the mass ratio of the added active silicic acid to the seed crystal is 2 to 8:1. For example, it can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or 8:1.

[0035] Preferably, the dripping time is 60-200 min. For example, it can be 60 min, 100 min, 150 min, or 200 min.

[0036] The dropping rate in this application is: mass of active silicic acid added / dropping time.

[0037] In this application, the rate of addition of active silicic acid during the second reaction is also a critical parameter. If the dropping rate is too fast or too slow, the resulting product will have an excessively large particle size, failing to meet the requirement of a small particle size (less than 10 nm). It will also lead to poor product stability and a tendency for agglomeration.

[0038] Preferably, the temperature of the second reaction is 95~105℃. The temperature can also be 98~100℃ or 98~102℃.

[0039] Preferably, the temperature of the second reaction is the same as the temperature of the first reaction.

[0040] Preferably, after the second reaction is completed, the mixture is kept at a warm temperature for 0.5 to 3 hours. Alternatively, it can be kept at a warm temperature for 1 to 2 hours, 0.5 to 2 hours, or 1 to 3 hours.

[0041] Preferably, concentration is achieved using one or more of ultrafiltration, vacuum distillation, and reverse osmosis. A second aspect of the invention provides a silica sol prepared by the method described above, wherein the silica particles in the silica sol have a particle size of 3-10 nm. For example, the particle size can be 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm.

[0042] Preferably, the concentration of the silica sol is 15-30 wt%. For example, it can be 15-28 wt% or 15-20 wt%. In this application, the concentration of silica sol refers to the mass concentration of silicon dioxide in the silica sol.

[0043] Preferably, after being stored at a temperature of 50~70℃ for 30~35 days, the particle size growth rate of silica in the silica sol is ≤5%. For example, the storage temperature can be 50℃, 60℃, or 70℃, and the number of days can be 30 days, 31 days, 32 days, 33 days, 34 days, or 35 days.

[0044] More specifically, after being stored at 60°C for 30 days, the particle size growth rate of silica in the silica sol is ≤5%.

[0045] Preferably, the conductivity of the silica sol is 2000~3500 μS / cm. For example, it can be 2800~3400 μS / cm, 2800~3500 μS / cm, or 2000~3400 μS / cm.

[0046] Preferably, the pH of the silica sol is 8.5~10.0. For example, it can be 8.5~9.6, 9.0~10, or 9.0~9.6.

[0047] A third aspect of the present invention provides the application of the silica sol as described above as a raw material component in the preparation of precision casting coatings, refractory material binders, and semiconductor polishing materials.

[0048] Beneficial effects:

[0049] This application provides a small-particle-size silica sol with excellent stability and its preparation method. This method employs a specific preparation method for active silicic acid (such as the flow rate of sodium silicate aqueous solution, resin dosage, and stirring conditions), combined with other parameters, to produce a silica sol with small particle size and excellent stability, enabling long-term stable storage. Furthermore, this method can introduce a second reaction to rationally control the particle size range of the silica sol product, achieving particle size diversity while maintaining a small particle size. By controlling the dropping rate during the second reaction and the pH of the reaction system, combined with other technical means, the prepared silica sol not only has small particle size and good diversity but also excellent stability, enabling long-term stable storage. Detailed Implementation

[0050] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0051] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0052] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0053] The ultrafiltration concentration in the following embodiments of this application refers to the use of spiral wound or hollow fiber ultrafiltration membrane separation equipment, wherein the molecular weight cutoff of the ultrafiltration membrane is 1000~10000 Da, preferably 2000~6000 Da, such as 2000 Da, 3000 Da, 4000 Da, 5000 Da, or 6000 Da.

[0054] The following embodiments of this application use 001×7 strong acid cation exchange resin, which is activated before use. The specific activation steps are as follows:

[0055] Resin pretreatment: Rinse the commercially available 001×7 strong acid cation exchange resin (Na type) repeatedly with deionized water to remove surface dust and broken particles until the wash water is clear and free of foam.

[0056] Acid conversion treatment: The pretreated resin is packed into an ion exchange column, and 5% sulfuric acid solution with 3 times the resin volume is passed through the resin layer at a flow rate of 2 times the column volume / hour to convert the resin to H form.

[0057] Wash to neutral: After acid conversion, rinse the resin with deionized water at a flow rate of 3 column volumes / hour until the pH of the effluent is 6.

[0058] Storage after activation: After activation, the H-type resin is soaked in deionized water for storage and later use.

[0059] The 001×7 strong acid cation exchange resin in this application has a pH range of 1 to 14, and its total exchange capacity is ≥4.0 mmol / g based on the dry basis of the resin.

[0060] The particle size in this application refers to the titrated particle size, and the test method is as follows: the test is carried out in accordance with the national standard HG / T 2521-2022 Industrial Silica Sol.

[0061] Example 1

[0062] This embodiment provides a specific method for preparing small-particle-size silica sol, including the following steps:

[0063] 1) Prepare 6 kg of sodium silicate aqueous solution with a concentration of 8.0 wt%. Pump the sodium silicate aqueous solution into a reactor containing 6 kg of 001×7 cation exchange resin at a flow rate of 5 kg / min (M / 1.2 min). Maintain a constant temperature of 25℃ and stir continuously for 0.8 h at a stirring speed of 200 rpm to carry out the ion exchange reaction and obtain active silicic acid with a concentration of 3.0 wt%.

[0064] 2) Take 1000g of active silicic acid and transfer it to a 5L reactor. Turn on the stirrer (200 rpm). Add 5wt% sodium hydroxide solution to adjust the pH of the system to 9.0 to carry out the first reaction. Heat the reactor to 100℃ and stir at a constant temperature for 36 minutes (200 rpm) to obtain seed crystals.

[0065] 3) Maintain the reactor temperature at 100℃ and the stirring speed at 200 rpm. Add active silicic acid dropwise to the seed crystals at a rate of 40 g / min (the mass ratio of active silicic acid to seed crystals is 4:1) for 100 min. During the dropwise addition, continuously add 5 wt% sodium hydroxide solution to maintain the pH of the system at 10.0. After the dropwise addition is complete, keep the mixture at this temperature for 2 hours to obtain the semi-finished product.

[0066] 4) After the semi-finished product is concentrated and dehydrated by ultrafiltration, a silica sol with a titration particle size of 7.32 nm and a concentration of 20 wt% is obtained.

[0067] Example 2

[0068] This embodiment provides a specific method for preparing small-particle-size silica sol, including the following steps:

[0069] 1) Prepare 120 kg of sodium silicate aqueous solution with a concentration of 10.0 wt%. Pump the sodium silicate aqueous solution into a reactor containing 120 kg of 001×7 cation exchange resin at a flow rate of 120 kg / min (M / 1min). Maintain a constant temperature of 25℃ and stir continuously for 0.6 h at a stirring speed of 150 rpm to carry out the ion exchange reaction and obtain active silicic acid with a concentration of 4.0 wt%.

[0070] 2) Take 95 kg of active silicic acid and transfer it to a 1000 L reactor. Turn on the stirrer (180 rpm). Add 10 wt% AMP to adjust the pH of the system to 9.5 to carry out the first reaction. Heat the reactor to 98 °C and stir at a constant temperature for 30 min (180 rpm) to obtain seed crystals.

[0071] 3) After the seed crystals are concentrated and dehydrated by ultrafiltration, a silica sol with a titration particle size of 3.8 nm and a concentration of 15 wt% is obtained.

[0072] Example 3

[0073] This embodiment provides a specific method for preparing small-particle-size silica sol, including the following steps:

[0074] 1) Prepare 800 kg of sodium silicate aqueous solution with a concentration of 10.0 wt%. Pump the sodium silicate aqueous solution into a reactor containing 800 kg of 001×7 cation exchange resin at a flow rate of 400 kg / min (M / 2 min). Maintain a constant temperature of 25℃ and stir continuously for 0.6 h at a stirring speed of 150 rpm to carry out the ion exchange reaction and obtain active silicic acid with a concentration of 4.0 wt%.

[0075] 2) Same as Example 2;

[0076] 3) Maintain the reactor temperature at 98℃ and the stirring speed at 180 rpm. Add active silicic acid dropwise to the seed crystals at a rate of 4.5 kg / min (the mass ratio of active silicic acid to seed crystals is 7:1) for 150 min. During the dropwise addition, continuously add 10 wt% AMP to maintain the pH of the system at 10.0. After the dropwise addition is complete, keep the mixture at this temperature for 2 hours to obtain the semi-finished product.

[0077] 4) After the semi-finished product is concentrated and dehydrated by ultrafiltration, a silica sol with a titration particle size of 8.89 nm and a concentration of 15 wt% is obtained.

[0078] Example 4

[0079] This embodiment provides a specific method for preparing small-particle-size silica sol, including the following steps:

[0080] 1) Prepare 5000 kg of sodium silicate aqueous solution with a concentration of 11.0 wt%. Pump the sodium silicate aqueous solution into a reactor containing 3500 kg of Tulsimer® T-42 H cation exchange resin at a flow rate of 1700 kg / min (M / 2.94 min). Maintain a constant temperature of 25°C and stir continuously for 0.9 h at a stirring speed of 150 rpm to carry out the ion exchange reaction and obtain active silicic acid with a concentration of 4.5 wt%.

[0081] 2) Take 500 kg of active silicic acid and transfer it to a 5000 L reactor. Turn on the stirrer (120 rpm). Add 25 wt% industrial grade ammonia water dropwise to adjust the pH of the system to 9.5 to carry out the first reaction. Heat the reactor to 100 °C and stir at a constant temperature for 24 min (120 rpm) to obtain seed crystals.

[0082] 3) Maintain the reactor temperature at 100℃ and the stirring speed at 120 r / min. Add active silicic acid dropwise to the seed crystals at a rate of 20 kg / min (the mass ratio of active silicic acid to seed crystals is 8:1) for 200 min. During the dropwise addition, continuously add 25 wt% industrial-grade ammonia water to maintain the pH of the system at 10.4. After the dropwise addition is complete, keep the mixture at this temperature for 1 hour to obtain a semi-finished product.

[0083] 4) After the semi-finished product is concentrated and dehydrated by ultrafiltration, a silica sol with a titration particle size of 9.94 nm and a concentration of 28 wt% is obtained.

[0084] Comparative Example 1

[0085] 1) Same as Example 1;

[0086] 2) The temperature for the first reaction was 25°C, and the remaining steps were the same as in Example 1;

[0087] 3) Same as Example 1;

[0088] 4) Same as Example 1.

[0089] Comparative Example 2

[0090] 1) Except for adjusting the amount of 001×7 cation exchange resin to 3 kg (the mass ratio of sodium silicate aqueous solution to 001×7 cation exchange resin is 1:0.5), the other steps are exactly the same as in Example 1.

[0091] The prepared active silicic acid was found to be whitish in color and exhibited gelation, making it impossible to proceed with further experiments.

[0092] Comparative Example 3

[0093] 1) Same as Example 1;

[0094] 2) Same as Example 1;

[0095] 3) Except that the pH of the system is 9.0 when adding the active silicon, the other steps are the same as in Example 1;

[0096] 4) Same as in Example 1; the semi-finished product is concentrated and dehydrated using an ultrafiltration device to obtain the target silica sol product.

[0097] Comparative Example 4

[0098] 1) Same as Example 1;

[0099] 2) Same as Example 1;

[0100] 3) Except for the addition of active silicon, where the dropping rate is 80 g / min and the dropping time is 50 minutes, the other steps are the same as in Example 1;

[0101] 4) Same as in Example 1; after the semi-finished product is concentrated and dehydrated by an ultrafiltration device, the target silica sol product is obtained.

[0102] Comparative Example 5

[0103] 1) Same as Example 1;

[0104] 2) Same as Example 1;

[0105] 3) Except for the addition of active silicon, where the dropping rate is 10 g / min and the dropping time is 400 minutes, the other steps are the same as in Example 1;

[0106] 4) Same as in Example 1. The semi-finished product is concentrated and dehydrated using an ultrafiltration device to obtain the target silica sol product.

[0107] Comparative Example 6

[0108] 1) Activated silicic acid is prepared using the conventional ion-column exchange method found in existing technologies. Specifically:

[0109] Prepare 120 kg of 10.0 wt% sodium silicate aqueous solution, pack an equal amount of 001×7 cation exchange resin into an ion exchange column, add the sodium silicate aqueous solution into the ion exchange column from one end at a flow rate of 6 kg / min (M / 20 min), and collect the prepared active silicic acid at the other end of the ion exchange column.

[0110] 2) Same as Example 2;

[0111] 3) Same as Example 2.

[0112] Comparative Example 7

[0113] 1) Except for adjusting the flow rate to 6 kg / min (M / 20 min), the rest of the steps are exactly the same as in Example 2.

[0114] The prepared active silicic acid was found to be whitish in color and exhibited gelation, making it impossible to proceed with further experiments.

[0115] The applicant conducted performance tests on the silica sols prepared in Examples 1-4, including pH value and conductivity. The specific results are shown in Table 1.

[0116] The pH value was tested according to the national standard HG / T 2521-2022 for industrial silica sol.

[0117] The conductivity test method is as follows: refer to the national standard GB / T 6908-2018 for testing.

[0118] The specific test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] As shown in Table 1, the silica sol provided by this application has a pH of 9.0~9.6 and a conductivity of 2800~3400 μS / cm, exhibiting good colloidal stability.

[0122] The applicant also conducted performance tests on the silica sols prepared in Examples 1-4 and Comparative Examples 1-7, including titration tests on particle size and stability. The specific results are shown in Table 2.

[0123] The test method for titration particle size is as follows: the test is conducted in accordance with the national standard HG / T 2521-2022 Industrial Silica Sol.

[0124] The stability test method is as follows: Before stable storage, the particle size of the silica sol is titrated using the method described above to obtain the initial particle size. Then, the silica sol is sealed and placed in a 60℃ oven for accelerated storage for 30 days. The state of the silica sol is observed, and the particle size after 30 days is measured. The particle size growth rate is calculated using the formula: (particle size after 30 days - initial particle size) / initial particle size × 100%. The smaller the particle size growth rate, the better the stability of the silica sol. Generally, a growth rate ≤ 5% is considered to indicate excellent particle size stability of the silica sol product.

[0125] Table 2

[0126]

[0127] As shown in Table 2, the silica sols prepared in Examples 1-4 of this application have small titration particle sizes, ranging from 3.8 to 9.94 nm, which meets the small particle size requirement of this application; moreover, they exhibit excellent stability. They show good storage stability at 60°C, with no gelation or aggregation occurring within 30 days, or even 35 days. The particle size growth rate is low, all less than or equal to 5%, meeting the requirement of excellent stability.

[0128] As can be seen from Comparative Example 1 and Example 1, compared with Example 1, Comparative Example 1 cannot achieve the preparation of small-particle-size, highly stable silica sol. The product obtained has a significantly larger particle size and poor stability, exhibiting slight gelation on day 8 and complete gelation on day 20, with a particle size increase rate of 48%, which does not meet the product requirements of this application. This indicates that the conditions during the first reaction can affect the performance of subsequent products, and temperature is an important characteristic parameter. If the temperature during the first reaction is too low, it will lead to the inability to form structurally stable and uniformly sized nanocrystals, resulting in uneven nucleation sites, secondary nucleation, and particle aggregation during the subsequent growth process. The final silica sol has a significantly larger particle size, wider distribution, and poor stability, and is prone to gelation and precipitation, making it impossible to prepare a small-particle-size, high-concentration, and highly stable silica sol product.

[0129] As can be seen from Comparative Example 2 and Example 1, the amount of resin used is a very important parameter when sodium silicate is mixed with resin for ion exchange, as it can affect the performance of the product. If too little resin is used, the generated active silicic acid will turn white and gelation will occur, making it impossible to proceed to the next step of the experiment and obtain the finished silica sol.

[0130] As can be seen from Comparative Example 3 and Example 1, compared with Example 1, Comparative Example 3 cannot achieve the preparation of highly stable silica sol. The product obtained has poor stability; when stored at 60°C, slight gelation occurs on the 12th day, and complete gelation occurs on the 30th day, with a particle size increase rate of 32%. This does not meet the product requirements of this application. This indicates that the pH value is an important condition parameter when adding active silicic acid a second time. If the pH of the reaction system during the second reaction is not within the range of 9.5~10.5 required by this application, and the pH is too low, the dissociation rate of active silicic acid will decrease, the concentration of free silicate ions will decrease, the condensation reaction will slow down, and uneven condensation will easily occur, resulting in uneven crystal nucleus size and wider distribution. At the same time, low pH results in insufficient negative charge on the surface of silica sol particles, weakening the repulsive force and making agglomeration easy, resulting in extremely poor uniformity and stability of the final product, making it impossible to prepare highly stable silica sol.

[0131] As can be seen from Comparative Examples 4-6 and Example 1, in the technical solution of this application, the dropping rate is a very important parameter during the secondary addition of active silicic acid, which can affect the performance of the product. Only within the scope of the technical solution of this application can the technical effect of this application be achieved.

[0132] If the dropping rate is too fast (as in Comparative Example 4), the final product will have excessively large particle size, noticeably cloudy color, and poor stability. Slight gelation occurs after 10 days of storage at 60℃, and complete gelation occurs after 25 days, with a particle size increase of 38%. It is impossible to prepare small-particle-size, highly stable silica sol. This may be because the excessively fast dropping rate prevents a large amount of active silicic acid from diffusing evenly within a unit time, leading to localized supersaturation and abnormal secondary nucleation, resulting in uneven crystal nucleus size and increased particle size. Simultaneously, the excessively rapid local condensation reaction results in too many active sites on the particle surface, making aggregation easy. This leads to poor uniformity and extremely poor stability in the final product, causing gel failure within a short period.

[0133] If the dropping rate is too slow (as in Comparative Example 5), the final product will have excessively large particle size, noticeably cloudy color, and poor stability. Slight gelation occurs after 11 days of storage at 60℃, and complete gelation occurs after 28 days, with a particle size increase rate of 35%. It is impossible to prepare small-particle-size, highly stable silica sol. This may be because the slow dropping rate results in an active silicic acid supply rate far lower than the seed crystal growth requirement, thus failing to meet the synchronous growth of all seed crystals. Some seed crystals grow excessively, while others grow slowly, leading to uneven crystal nucleus size, increased particle size, and wider distribution. Simultaneously, the slow dropping rate prolongs the dropping time, causing the seed crystals to remain in the high-temperature alkaline environment for too long, making them prone to secondary agglomeration and excessive condensation, resulting in a loose particle structure and decreased stability.

[0134] As can be seen from Comparative Example 6 and Example 2, the technical solution of this application is completely different from the conventional ion column exchange method used in the prior art. The preparation method of active silicic acid in this application is also a crucial step. Only by using the preparation method of active silicic acid described in this application, i.e., using a specific flow rate (the mixing speed of sodium silicate aqueous solution and resin) combined with a specific ion exchange method (such as stirring, stirring temperature, time, etc.), can the technical effect of this application be obtained. Furthermore, compared with Example 2, the product in Comparative Example 6 has poor stability; gelation occurs after storage at 60°C for 25 days, and the particle size increase rate is 15%, failing to achieve the preparation of the highly stable silica sol described in this application.

[0135] As can be seen from Comparative Example 7 and Example 2, the speed at which sodium silicate is added to the mixing tank and mixed with the resin can significantly affect the performance of the generated silica sol. Only within the speed range specified in this application can the technical effect of this application be achieved. If the sodium silicate aqueous solution is added to the mixing tank too slowly, the generated active silicic acid will turn white and gelation will occur, making it impossible to proceed to the next experiment and obtain the finished silica sol.

[0136] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing small-particle-size silica sol, characterized in that, Includes the following steps: Sodium silicate aqueous solution is stirred and mixed in a stirring tank containing resin to carry out ion exchange, thereby obtaining active silicic acid; Take a portion of active silicic acid, add an alkaline substance to it to make the pH 8.5~9.5 to carry out the first reaction, and obtain seed crystals; The silica sol was obtained after concentration; The sodium silicate aqueous solution is added to the stirring tank at a rate of M / 3min to M / 1min, where M is the mass of the sodium silicate aqueous solution.

2. The preparation method according to claim 1, characterized in that, The concentration of the sodium silicate aqueous solution is 7.0 wt%~12.0 wt%; And / or, the mass ratio of the sodium silicate aqueous solution to the resin is 1:0.8~2; And / or, the resin is a strong acid cation exchange resin; And / or, the ion exchange reaction time is 0.5~1h; And / or, the stirring speed during ion exchange is 150~300 rpm.

3. The preparation method according to claim 2, characterized in that, Based on the dry basis of the resin, the total exchange capacity of the resin is ≥4.0 mmol / g; And / or, the resin is selected from one or more of 001×7, 001×8, D001, Tulsimer® T-42 H, and Amberlyst 15.

4. The preparation method according to claim 1, characterized in that, The alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, ammonia, monoethanolamine, diethanolamine, isopropylamine, dimethylenetriamine, and 2-amino-2-methyl-1-propanol; And / or, the concentration of the alkaline substance is 5-30 wt%; And / or, when adding alkaline substances and carrying out the first reaction, stirring is performed at a speed of 100~300 rpm; And / or, after obtaining the seed crystal, the process further includes adding active silicic acid dropwise to the seed crystal to carry out a second reaction, and after the second reaction is completed, the concentration is carried out.

5. The preparation method according to claim 1, characterized in that, The temperature of the first reaction is 95~105℃; And / or, the seed crystals have a particle size of 3~5nm; And / or, concentration is carried out using one or more of ultrafiltration, vacuum distillation, and reverse osmosis.

6. The preparation method according to claim 4, characterized in that, During the second reaction, the alkaline substance is continuously added to maintain the pH of the reaction system at 9.5-10.

5. And / or, during the second reaction, the mass ratio of the added active silicic acid to the seed crystal is 2~8:1; And / or, the dripping time is 60~200 min.

7. The preparation method according to claim 4, characterized in that, The temperature for the second reaction is 95~105℃; And / or, the temperature of the second reaction is the same as the temperature of the first reaction; And / or, after the second reaction is completed, keep warm and mature for 0.5 to 3 hours.

8. A silica sol prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The silica particles in the silica sol have a diameter of 3-10 nm.

9. The silica sol according to claim 7, characterized in that, The concentration of the silica sol is 15~30 wt%; After being stored at 50-70℃ for 30-35 days, the particle size increase rate of silica in the silica sol is ≤5%; The conductivity of the silica sol is 2000~3500 μS / cm; The pH of the silica sol is 8.5~10.

0.

10. The use of silica sol as a raw material component as described in any one of claims 1 to 7 in the preparation of precision casting coatings, refractory material binders, and semiconductor polishing materials.

Images