Small-particle-size silica sol as well as preparation method and application thereof

Abstract

The embodiment of the invention provides small-particle-size silica sol as well as a preparation method and application thereof. The preparation method comprises the following steps: adding water glass into a silicic acid solution to obtain a mixed solution; controlling the pH value of the mixed solution to be 7-8.5, and stirring for reaction to obtain a seed crystal solution; adding a strong alkali solution into the seed crystal solution, controlling the pH value of the solution to be 9-12, and stirring for reaction to obtain a silica sol dilute colloid; carrying out heat preservation reaction and acidizing treatment on the silica sol dilute colloid to obtain acidic silica sol; and adding an aluminum salt solution into the acidic silica sol, and reacting to obtain the small-particle-size silica sol. According to the embodiment of the invention, the specific alkali reagent is adopted, the early-stage synthesis process of the silica sol can be carried out under the condition of normal temperature through a method for controlling the pH value in a segmented manner, the situation that the particle size of the silica sol is increased too fast and exceeds the target range of 4-6nm due to heating can be avoided, and meanwhile, the prepared small-particle-size silica sol also has higher stability.

Description

Technical Field

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

[0002] Silica sol is a colloid formed by uniformly dispersing silica particles with a particle size in the range of 4-120 nm in water or other dispersants. Silica sol with a particle size in the range of 4-10 nm is considered to be small-particle-size silica sol.

[0003] Currently, small-particle-size silica sols, with a particle size of only 4-10 nm, possess a much higher specific surface area than silica sols of other particle sizes, making them suitable as drug carriers for controlled drug release. Furthermore, small-particle-size silica sols exhibit advantages such as high-temperature stability, strong wear resistance, and good thermal conductivity, leading to their widespread application in the aerospace industry.

[0004] However, existing small-particle-size silica sols generally have the following drawbacks: 1. The synthesis process of small-particle-size silica sols using the ion exchange method requires the addition of alcohols, aldehydes, etc. as polymerization inhibitors, resulting in the final product containing trace amounts of polymerization inhibitors; 2. The particle size can be controlled by controlling the raw material formulation using elemental silica hydrolysis, but since it is a one-time feeding, silica sols of other particle sizes will be generated simultaneously; 3. The elemental silica hydrolysis method requires high-purity silica powder, which is expensive, and the finished product needs to be deeply filtered to remove residual silica powder, otherwise the product color will be dark.

[0005] Therefore, optimizing the preparation method of small-particle-size silica sol is an urgent problem to be solved in this field. Summary of the Invention

[0006] The purpose of this disclosure is to provide a small-particle-size silica sol, its preparation method, and its uses.

[0007] To achieve the above objectives, the present disclosure proposes the following technical solutions:

[0008] In a first aspect, embodiments of this disclosure provide a method for preparing small-particle-size silica sol, the method comprising:

[0009] Water glass is added to a silicic acid solution to obtain a mixed solution; the pH of the mixed solution is controlled at 7-8.5, and the reaction is stirred to obtain a seed crystal solution;

[0010] A strong alkaline solution is added to the seed crystal solution, and the pH value of the solution is controlled to be 9-12. The reaction is stirred to obtain a dilute silica sol colloid.

[0011] Acidic silica sol is obtained by reacting dilute silica sol with heat and acidification.

[0012] An aluminum salt solution is added to an acidic silica sol, and a small-particle-size silica sol is obtained by the reaction.

[0013] In one embodiment, the strong alkaline solution is a NaOH solution.

[0014] As one implementation method, the silica sol colloid is subjected to a heat preservation reaction and acidification treatment to obtain an acidic silica sol, comprising:

[0015] Alkaline silica sol is obtained by heating the dilute silica sol to 50-85℃ and maintaining the temperature for reaction.

[0016] Alkaline silica sol is acidified by cation exchange resin to obtain acidic silica sol.

[0017] As one embodiment, the step of adding an aluminum salt solution to an acidic silica sol and reacting to obtain a small-particle-size silica sol includes:

[0018] An aluminum salt solution is added to an acidic silica sol, the molar ratio of Al to Si is controlled at 0.1-0.5, and the mixture is heated to 50-85℃ and kept at this temperature to obtain a small-particle-size silica sol.

[0019] In one embodiment, the aluminum salt solution is an aluminum sulfate solution.

[0020] As one embodiment, the method for preparing the silicic acid solution includes:

[0021] An acid solution is added to the cation exchange resin, and after activation, the cation exchange resin is rinsed with deionized water to obtain an acidic cation exchange resin.

[0022] Water glass is added to an acidic cation exchange resin, and a silicic acid solution is obtained by the reaction.

[0023] In one embodiment, the acid solution is dilute sulfuric acid and / or dilute hydrochloric acid.

[0024] Secondly, embodiments of this disclosure provide a small-particle-size silica sol, which is prepared using the preparation method described in the first aspect.

[0025] In one embodiment, the particle size of the small-particle-size silica sol is 4-6 nm.

[0026] Thirdly, embodiments of this disclosure propose the use of the small-particle-size silica sol described in the second aspect in the preparation of targeted drug carriers, catalytic reaction carriers, or chip packaging and dielectric materials.

[0027] Compared with the prior art, the embodiments of this disclosure have at least the following beneficial effects:

[0028] In this embodiment, small-particle-size silica sol is prepared by segmented pH control. First, a silica solution is added to a reaction vessel in one step, followed by the addition of water glass to control the pH of the mixture within a weakly alkaline range of 7-8.5, allowing the silica solution to initially polymerize into seed crystals with smaller particle sizes. Second, a stronger alkaline solution is added to control the pH within a range of 9-10. Under these conditions, the remaining silica can directionally deposit SiO2 on the surface of the existing seed crystals, promoting particle growth while inhibiting the formation of new nuclei. Then, the mixture is aged by a heat-preserving reaction to obtain silica sol with a particle size of 4-6 nm.

[0029] Therefore, the present invention employs a specific alkaline reagent and controls the pH value in stages, so that the early synthesis process of silica sol can be carried out at room temperature. This avoids the silica sol particle size from growing too fast due to heating, exceeding the target range of 4-6 nm, while the resulting small-particle-size silica sol also has higher stability.

[0030] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of this disclosure. Attached Figure Description

[0031] Figure 1 A schematic diagram of the small-particle-size silica sol prepared in Example 3 is shown. Detailed Implementation

[0032] The technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this disclosure, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0033] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0034] It should also be understood that the terminology used in this specification of embodiments is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this disclosure. As used in this specification of embodiments and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0035] The following explanations of some of the terms and materials used in this embodiment will be provided to facilitate understanding by those skilled in the art.

[0036] Water glass: Sodium silicate (sodium silicate) aqueous solution.

[0037] The small-particle-size silica sol of this embodiment, its preparation method, and its uses will be described in detail below.

[0038] First, let me explain the method for preparing small-particle-size silica sol in the first aspect of this embodiment.

[0039] Preparation method of small particle size silica sol

[0040] In existing technologies, small-particle-size silica sols generally have the following drawbacks: 1. The synthesis process of small-particle-size silica sols using the ion exchange method requires the addition of alcohols, aldehydes, etc., as polymerization inhibitors, resulting in the final product containing trace amounts of polymerization inhibitors; 2. While the particle size can be controlled by adjusting the raw material formulation using elemental silica hydrolysis, since it involves a single feeding, silica sols of other particle sizes will be generated simultaneously; 3. The elemental silica hydrolysis method requires high-purity silica powder, which is expensive, and the finished product needs to be deeply filtered to remove residual silica powder, otherwise the product will have a dark color.

[0041] In view of this, this embodiment proposes a method for preparing small-particle-size silica sol, which includes the following steps:

[0042] (S1) Add water glass to the silicic acid solution to obtain a mixed solution; control the pH of the mixed solution to 7-8.5 (preferably 7.55-8.35), and stir the reaction to obtain a seed solution.

[0043] In step (S1), the silica solution is used as a base to initially polymerize into seed crystals (nuclei) with a smaller particle size in a weakly alkaline environment, so as to avoid subsequent particle size disorder or excessively large particle size.

[0044] Specifically, in this embodiment, the pH value of the mixture is controlled at 7-8.5 using water glass. The addition of water glass not only creates a weakly alkaline environment but also increases the polymerization of the monomer HSiO3 in the system. - and HSiO3 2- The concentration; under these system conditions, step (S1) can be carried out at room temperature and polymerize into seed crystals with smaller particle size and narrower (more uniform) particle size distribution, laying the foundation for subsequent uniform growth and the stability of silica sol.

[0045] Meanwhile, through relevant experiments in this embodiment, it was found that in step (S1), using other alkaline reagents, such as ammonia solution or strong alkaline solution (such as NaOH solution), will result in a significant decrease in the stability of the final silica sol.

[0046] (S2) Add a strong alkaline solution to the seed crystal solution, control the pH value of the solution to 9-12, and stir the reaction to obtain a silica sol dilute colloid.

[0047] Next, in step (S2), a strong alkaline solution is directly added to the seed crystal solution to raise the pH value of the system to 9-12, i.e., medium to strong alkalinity. Under these conditions, the remaining silicic acid can be directionally deposited on the surface of the existing seed crystals to promote particle growth while inhibiting the formation of new nuclei.

[0048] Therefore, based on the seed crystals formed in step (S1), step (S2) is beneficial to promote the further uniform growth of the seed crystal particles, which can reduce small particles and avoid the formation of large-particle silica sol due to excessively rapid particle size growth, thereby improving stability (avoiding gelation or delamination).

[0049] Based on this, this embodiment lays the foundation for obtaining small-particle-size silica sol with suitable particle size and better stability by controlling the pH value of steps (S1) and (S2) in subsequent heat preservation and curing.

[0050] (S3) Acidic silica sol is obtained by heat preservation reaction and acidification treatment of dilute silica sol.

[0051] In step (S3), the silica sol dilute colloid from step (S2) is cured through a heat preservation reaction. During the curing process, small particles are more easily dissolved (releasing silicate ions) due to their high surface energy, while large particles have low surface energy, and silicate ions preferentially deposit on their surfaces, further homogenizing the particle size (narrowing the particle size distribution). Secondly, in a moderately alkaline environment, the electrostatic repulsion between particles is strong, which can effectively inhibit agglomeration.

[0052] In this step, the alkaline silica sol is obtained after the heat treatment and curing reaction. As those skilled in the art know, alkaline silica sol is mainly used in specific occasions that require high negative charge or are alkaline environments, and its application field is relatively narrow.

[0053] To further expand the application scenarios of silica sol, step (S3) further acidifies the alkaline silica sol to obtain acidic silica sol with wider applications.

[0054] In the acidification process of step (S3), Na ions in the alkaline silica sol can be effectively removed to obtain acidic silica sol.

[0055] Understandably, based on steps (S1) and (S2), the alkaline silica sol and acidic silica sol prepared in step (S3) have better stability than conventional alkaline silica sol and acidic silica sol.

[0056] (S4) Add aluminum salt solution to acidic silica sol and react to obtain small particle size silica sol.

[0057] In step (S4), the acidic silica sol is modified by adding an aluminum salt solution; that is, in this embodiment, an aluminum salt solution is used as a modification solution to modify the surface of the acidic silica sol, thereby further enhancing its stability and obtaining a small-particle-size silica sol with higher stability.

[0058] Based on the above steps, this embodiment can prepare small-particle-size silica sol (acidic silica sol) with a target particle size of 4-6 nm and higher stability.

[0059] In summary, this embodiment prepares small-particle-size silica sol by segmented pH control. First, a silica solution is added to the reactor in one step, followed by the addition of water glass to control the pH of the mixture within a weakly alkaline range of 7-8.5, allowing the silica solution to initially polymerize into seed crystals with smaller particle size and more uniform distribution. Second, a stronger alkaline solution is directly added to control the pH within the range of 9-10. Under these conditions, the remaining silica can directionally deposit SiO2 on the surface of the existing seed crystals, promoting particle growth while inhibiting the formation of new nuclei. Finally, the particles are further homogenized through a heat-preserving reaction to obtain silica sol with a particle size of 4-6 nm.

[0060] Therefore, this embodiment uses a specific alkaline reagent and controls the pH value in stages, so that the early synthesis process of silica sol can be carried out at room temperature. This avoids the silica sol particle size from growing too fast due to heating, exceeding the target range of 4-6 nm, and the resulting small-particle-size silica sol also has higher stability.

[0061] It is understood that in this embodiment, the strong alkali solution is more alkaline than the weak alkali solution.

[0062] In step (S1), the water glass can be considered a weak alkaline solution, which can control the pH value of the system to 7-8.5 (weakly alkaline environment); while in step (S2), a strong alkaline solution is added, the purpose of which is to quickly change the weak alkaline environment to a medium-strong alkaline environment, that is, to increase the pH value of the system, so as to promote the rapid formation of silica sol.

[0063] In one embodiment, the strong alkaline solution is a NaOH solution.

[0064] In a preferred embodiment, the water glass contains 5%-10% SiO2 by mass and the NaOH solution contains 3%-15% by mass.

[0065] For example, the mass content of SiO2 in the water glass is 5%, 6%, 7%, 8%, 9%, or 10%; the mass fraction of the NaOH solution can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0066] The following will further explain the relevant steps of the above preparation method.

[0067] In step (S3), the dilute silica sol is subjected to a heat preservation reaction and acidification treatment to obtain acidic silica sol, specifically including:

[0068] (S31) Heat the silica sol dilute colloid to 50-85℃ and keep it at that temperature to obtain alkaline silica sol;

[0069] (S32) After acidification treatment with cationic resin, alkaline silica sol is obtained as acidic silica sol.

[0070] As mentioned above, in step (S31), the silica sol dilute colloid from step (S2) is aged by a heat preservation reaction; typically, the heat preservation reaction time is 30-120 min, preferably 40-60 min.

[0071] In step (S32), this embodiment uses cationic resin to acidify alkaline silica sol. Compared with direct acidification with acid solution, this embodiment can not only avoid the impact of residual sodium salt on stability after direct acidification, but also effectively improve the stability of acidic silica sol.

[0072] Therefore, this embodiment can produce small-particle-size silica sol with higher stability.

[0073] The cation exchange resin can be a conventional cation exchange resin, such as Rohm and Haas's AMBERJET1200Na cation exchange resin.

[0074] The steps (S4) of this implementation will be further explained below.

[0075] In step (S4), an aluminum salt solution is added to the acidic silica sol, and the reaction yields a small-particle-size silica sol, specifically including:

[0076] (S41) Add aluminum salt solution to acidic silica sol and control the molar ratio of Al to Si to be 0.1-0.5;

[0077] (S42) Heat to 50-85℃ and keep warm to obtain small-particle-size silica sol.

[0078] The aluminum salt solution added in step (S41) is a modification solution. Its purpose is to modify the surface of the acidic silica sol, thereby further enhancing its stability and obtaining a small-particle-size silica sol with higher stability.

[0079] Next, in step (S42), the silica sol from the surface step (S41) is further matured to obtain a small-particle-size silica sol with a uniform target particle size distribution of 4-6 nm and higher stability.

[0080] Typically, the heat treatment (cooking) time is 30-120 minutes, preferably 40-60 minutes.

[0081] In one embodiment, the aluminum salt solution is an aluminum sulfate solution.

[0082] In this embodiment, the mass fraction of the aluminum sulfate solution is 20%-50%. Exemplarily, the mass fraction of the aluminum sulfate solution can be 20%, 21%, 22%, 23%, 24%, 25%, 30%, 32%, 34%, 36%, 38%, 40%, 41%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%.

[0083] The silica solution of this embodiment will be further described below.

[0084] The silicic acid solution in this embodiment can be a known existing silicic acid solution, or it can be prepared by existing conventional methods.

[0085] As one embodiment, the method for preparing the above-mentioned silicic acid solution includes:

[0086] (S01) Add an acid solution to the cation exchange resin, activate it, and then rinse the cation exchange resin with deionized water to obtain an acidic cation exchange resin.

[0087] (S02) Water glass is added to the acidic cation exchange resin, and the reaction yields a silicic acid solution.

[0088] In a preferred embodiment, in step (S02), the water glass used contains 5%-10% SiO2 by mass.

[0089] In step (S01), after activation, the cation exchange resin is washed with deionized water; for example, the washing is required until no SO4 is present in the effluent. 2- (No white precipitate was detected with BaCl2 solution), and the pH remained stable at 4-5 (ensuring H+). + The resin is activated to prevent residual acid from causing localized over-acidity.

[0090] Next, in step (S02), H is used + Type I resin (acidic cation exchange resin) and Na+ in water glass + Exchange occurs, producing a silicic acid solution (active silicic acid).

[0091] In one embodiment, the acid solution is dilute sulfuric acid and / or dilute hydrochloric acid, preferably dilute sulfuric acid, and more preferably dilute sulfuric acid with a concentration of 2%-15%.

[0092] The preparation process of silicic acid solution will be further clarified below using specific preparation methods.

[0093] (S01) at 5m 3 Add 0.8-1m into the reactor 3 Rohm and Haas cation exchange resins (such as AMBERJET 1200Na) are activated with 2%-15% sulfuric acid. After activation, the cation exchange resin is rinsed with deionized water to obtain an acidic cation exchange resin with a pH of 4-5.

[0094] (S02) Add 0.3m to the acidic cation exchange resin. 3 Water glass (SiO2 content of 10%) is reacted to remove sodium ions and other metal ions, resulting in an active silicic acid solution with a concentration of about 6%, which is then filtered for later use.

[0095] Next, the small-particle-size silica sol of the second aspect will be explained.

[0096] Small particle size silica sol

[0097] Based on the description in the first aspect, the small-particle-size silica sol prepared in this embodiment has a suitable particle size range, and the small-particle-size silica sol has higher stability.

[0098] Preferably, from the perspective of particle size, the particle size of the small-particle silica sol is 4-6 nm; from the perspective of stability, the small-particle silica sol exhibits stability for at least 35 days at 50°C.

[0099] It should be noted that the stability at 50°C mentioned in this embodiment refers to the fact that when small-particle-size silica sol is placed in an oven at 50°C, its appearance does not change; for example, there is no layering, no precipitation, no flocculation (it remains transparent and does not become cloudy, white, or gel-like clumps), and no abnormal color (the originally colorless and transparent silica sol does not turn yellow or darken).

[0100] Next, the use of the third aspect of this embodiment will be explained.

[0101] Applications of small-particle-size silica sol

[0102] Given that the small-particle-size silica sol prepared in this embodiment possesses a suitable particle size range and higher stability, and considering its high specific surface area, excellent dispersibility, strong reactivity, and dense packing ability, small-particle-size silica sol exhibits irreplaceable advantages in fields requiring high precision and high performance. Therefore, the small-particle-size silica sol of this embodiment can be used to prepare targeted drug carriers, catalytic reaction carriers, or chip packaging and dielectric materials.

[0103] For example, in the field of chip packaging and dielectric materials, small-particle-size silica sol, as an epoxy resin filler, can fill the micro-gaps between the chip and the substrate, reducing the coefficient of thermal expansion and improving packaging reliability through dense packing. Alternatively, small-particle-size silica sol can be compounded with organosilanes and sintered at high temperature to form a porous SiO2 film, which is used for insulation of the chip interconnect layer and reduces signal delay.

[0104] Small-particle-size silica sols can also be used to prepare targeted drug carriers to achieve controlled drug release. For example, surface modifications of small-particle-size silica sols with PEG and targeted peptides (such as RGD) can penetrate tumor cell membranes, increase drug loading, and thus improve the inhibition rate of breast cancer cells.

[0105] Meanwhile, the high specific surface area of ​​small-particle-size silica sol can significantly increase the active sites of the catalyst, thus making it suitable for use as a catalytic reaction support.

[0106] In addition, small-particle-size silica sol has advantages such as high-temperature stability, strong wear resistance, and good thermal conductivity, which makes it widely used in the aerospace field.

[0107] The present disclosure will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustration / explanation only and are not intended to limit the scope of the present disclosure.

[0108] Unless otherwise specified, all materials, reagents and instruments used in the following embodiments are commercially available.

[0109] In the following examples and comparative examples, the silicic acid solutions were prepared according to the following preparation method.

[0110] Methods for preparing silicic acid solutions include:

[0111] (1) At 5m 3 1m 3 Rohm and Haas cationic resin (AMBERJET)

[0112] 1200Na), used (dosage is 1m) 3 -1.5m 3 The cation exchange resin was activated with 10% sulfuric acid, and then rinsed with deionized water to obtain an acidic cation exchange resin with a pH of 4.

[0113] (2) Add 0.3m to the acidic cation exchange resin. 3 Water glass (SiO2 content 10%) is reacted to remove sodium ions and other metal ions, resulting in a 6% silica solution, which is then filtered for later use.

[0114] Next, based on the prepared silica solution, the following examples and comparative experiments were conducted.

[0115] Example 1

[0116] Example 1 provides a method for preparing small-particle-size alkaline silica sol, comprising:

[0117] The reactor was kept at room temperature, and 1.4m 3 Silicate solution (6% concentration) was added to 3m 3 Keep stirring inside the reactor;

[0118] Quickly add water glass (SiO2 content 6.62%), monitor the pH value to 7.55, and stir for 1 hour;

[0119] Slowly add a 6.35% NaOH solution, monitor the pH value to 9.23, and stir for 1 hour;

[0120] Heating to 62.3℃ and holding for 45 minutes yielded small-particle-size alkaline silica sol.

[0121] Example 2

[0122] This embodiment provides a method for preparing small-particle-size alkaline silica sol, including:

[0123] The reactor was kept at room temperature, and 1.4m 3 Silicate solution (6% concentration) was added to 3m 3 Keep stirring inside the reactor;

[0124] Quickly add water glass (SiO2 content 6.62%), monitor the pH value to 8.35, and stir for 1 hour;

[0125] Slowly add a 6.35% NaOH solution, monitor the pH value to 9.63, and stir for 1 hour;

[0126] Heating to 62.7℃ and holding for 45 minutes yielded small-particle-size alkaline silica sol.

[0127] Comparative Example 1

[0128] Comparative Example 1 provides a method for preparing an alkaline silica sol, comprising:

[0129] The reactor was kept at room temperature, and 1.4m 3 Silicate solution (6% concentration) was added to 3m 3 Keep stirring inside the reactor;

[0130] Slowly add a 6.35% NaOH solution, monitor the pH value to be 10.67, and stir for 1 hour;

[0131] Heat to 60.1℃ and maintain the temperature for 45 minutes to obtain alkaline silica sol.

[0132] Comparative Example 2

[0133] Comparative Example 2 provides a method for preparing an alkaline silica sol, comprising:

[0134] The reactor was kept at room temperature, and 1.4m 3 Silicate solution (6% concentration) was added to 3m 3 Keep stirring inside the reactor;

[0135] Quickly add a 6.35% NaOH solution, monitor the pH value to 7.36, and stir for 1 hour;

[0136] Slowly add a 6.35% NaOH solution, monitor the pH value until it reaches 10.33, and stir for 1 hour.

[0137] Heat to 64.3℃ and maintain the temperature for 45 minutes to obtain alkaline silica sol.

[0138] Comparative Example 3

[0139] Comparative Example 3 provides a method for preparing an alkaline silica sol, comprising:

[0140] The reactor was kept at room temperature, and 1.4m 3 Silicate solution (6% concentration) was added to 3m 3 Keep stirring inside the reactor;

[0141] Quickly add a 10.11% ammonia solution, monitor the pH value to 7.77, and stir for 1 hour;

[0142] Slowly add a 6.35% NaOH solution, monitor the pH value to 9.88, and stir for 1 hour;

[0143] Heat to 62.5℃ and maintain the temperature for 45 minutes to obtain alkaline silica sol.

[0144] Example 3

[0145] Example 3 further acidifies and modifies the alkaline silica sol obtained in Example 1 to obtain the final small-particle-size silica sol (acidic silica sol), specifically including:

[0146] The silica sol obtained in Example 1 was subjected to Na removal treatment using a cationic resin (AMBERJET 1200Na), and the silica sol was simultaneously acidified using the same cationic resin to a pH of 2.58.

[0147] Next, a 30% aluminum sulfate solution was added, and the Al / Si molar ratio was controlled at 0.15. The mixture was heated to 60.7°C and kept warm for 45 minutes to obtain the modified silica sol.

[0148] Comparative Example 4

[0149] Similar to Example 3, Comparative Example 4 further acidifies and modifies the alkaline silica sol obtained in Example 1 to obtain the final small-particle-size silica sol (acidic silica sol), specifically including:

[0150] The silica sol prepared in Example 1 was directly acidified with 5% sulfuric acid by mass, first to pH 7.45, and then to pH 2.24.

[0151] Next, a 30% aluminum sulfate solution was added, and the Al / Si molar ratio was controlled at 0.15. The mixture was heated to 60.5℃ and kept warm for 45 minutes to obtain the modified silica sol.

[0152] The silica sols prepared in Examples 1-3 and Comparative Examples 1-4 were then tested for their effects, including pH value, SiO2 content, particle size, appearance, and stability at 50°C. The test results are shown in Table 1 below.

[0153] Among them, pH value, SiO2 content, particle size and appearance were tested according to the standard "HG / T 2521-2022 Industrial Silica Sol"; stability at 50℃ was specifically tested by preheating the oven to 50℃, placing the silica sol in the oven, and observing and recording the gelation time of the silica sol.

[0154] Table 1: Test results of Examples 1-3 and Comparative Examples 1-4.

[0155] sample pH value SiO2 content (%) Particle size / nm Appearance 50℃ Oven Stability Example 1 9.44 15.12 4.19 transparent 92 days Example 2 9.63 15.33 4.38 transparent 87 days Comparative Example 1 10.98 15.01 3.69 transparent 14 days Comparative Example 2 10.88 15.00 4.43 transparent 17 days Comparative Example 3 9.88 14.88 4.58 transparent 6 days Example 3 2.79 15.44 5.59 transparent 35 days Comparative Example 4 2.35 15.04 5.30 transparent 3 days

[0156] in, Figure 1 A schematic diagram of the silica sol prepared in Example 3 is shown.

[0157] In Table 1, the silica sols prepared in Examples 1 and 2, and Comparative Examples 1-3 are alkaline silica sols; the silica sols prepared in Examples 3 and 4 are acidic silica sols.

[0158] According to the test results in Table 1, in Examples 1 and 2, the method of segmented pH control in this example allows the synthesis process of silica sol to be carried out at room temperature. This avoids the silica sol particle size from growing too fast due to heating, exceeding the target range of 4-6 nm, and the resulting small-particle-size silica sol also has higher stability. Specifically, Example 1 has a stability of 92 days at 50°C, and Example 2 has a stability of 87 days at 50°C.

[0159] Further comparing Example 1 and Comparative Example 1, the Comparative Example used NaOH solution to directly adjust the pH to 10.67. Under these conditions, the polymerization reaction of silicate remained in a "highly active" state. The initially formed sol continued to slowly polymerize during subsequent storage, gradually cross-linking between particles to form a three-dimensional network, eventually transforming from a sol into a gel, and its stability could not be maintained for a long time. Simultaneously, excessively high OH... - It may also erode the Si-O-Si bonds on the particle surface, causing some particles to dissolve or fragment, thus compromising structural stability. Therefore, compared with the segmented pH control in Example 1, the silica sol prepared in Comparative Example 1 showed a significant decrease in stability, exhibiting stability for only 14 days at 50°C.

[0160] Further comparing Example 1 with Comparative Examples 2 and 3, in the weakly alkaline stage, Comparative Example 2 used NaOH solution and Comparative Example 3 used ammonia solution; Among them, Comparative Example 2 used NaOH solution to adjust the pH value. Because its alkalinity is strong, it directly contacted the active silicic acid solution to produce gel particles, resulting in poor stability of the final product, which only had a stability of 17 days at 50°C.

[0161] Comparative Example 3 used ammonia solution to adjust the pH value because the SiO2 content in its final product could not reach the required range of 15%; at the same time, the final product had poor stability, with only 6 days of stability at 50°C.

[0162] Please refer to Table 1 for the test results of the acidic silica sols prepared in Example 3 and Comparative Example 4. Example 3 uses cationic resin to acidify alkaline silica sol, which not only avoids the impact of excessive residual Na salt on stability after direct acidification, but also effectively improves the stability of acidic silica sol, which exhibits a stability of 35 days at 50°C.

[0163] In contrast, the acidic silica sol in Example 4, due to the direct use of sulfuric acid for acidification, could not effectively remove sodium salts. Furthermore, the strong acidity of sulfuric acid not only neutralized the surface charge of the silica sol particles but also released SO42-. 2- This also strongly compresses the double layer, and under multiple effects, the electrostatic repulsion between particles is significantly weakened, ultimately leading to a sharp decline in the stability of the silica sol, which only has a stability of 3 days at 50°C.

[0164] In summary, firstly, this embodiment employs a specific alkaline reagent and a segmented pH control method, allowing the initial synthesis of silica sol to be carried out at room temperature. This avoids excessively rapid particle size growth due to heating, preventing the particle size from exceeding the target range of 4-6 nm. Simultaneously, the resulting small-particle-size silica sol exhibits higher stability. Secondly, this embodiment uses a cationic resin to acidify the alkaline silica sol. Compared to direct acidification with an acid solution, this embodiment not only avoids the impact of residual sodium salts on stability after direct acidification but also effectively improves the stability of the acidic silica sol.

[0165] The technical solutions provided by the embodiments of this disclosure have been described in detail above. Specific examples have been used in this document to illustrate the principles and implementation methods of the embodiments of this disclosure. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of this disclosure. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of this disclosure. Therefore, the content of this specification should not be construed as a limitation of this disclosure.

Claims

1. A method for producing a small-particle-size silica sol, characterized by, The preparation method includes: Water glass is added to a silicic acid solution to obtain a mixed solution; the pH of the mixed solution is controlled at 7-8.5, and the reaction is stirred to obtain a seed crystal solution; A strong alkaline solution is added to the seed crystal solution, and the pH value of the solution is controlled to be 9-12. The reaction is stirred to obtain a dilute silica sol colloid. Acidic silica sol is obtained by reacting dilute silica sol with heat and acidification. An aluminum salt solution is added to an acidic silica sol, and a small-particle-size silica sol is obtained by the reaction.

2. The production method according to claim 1, characterized by, The strong alkaline solution is a NaOH solution.

3. The preparation method according to claim 1, characterized in that, The silica sol colloid is subjected to a heat preservation reaction and acidification treatment to obtain acidic silica sol, comprising: Alkaline silica sol is obtained by heating the dilute silica sol to 50-85℃ and maintaining the temperature for reaction. Alkaline silica sol is acidified by cation exchange resin to obtain acidic silica sol.

4. The production method according to claim 1, characterized by, The process of adding an aluminum salt solution to an acidic silica sol to react and obtain a small-particle-size silica sol includes: An aluminum salt solution is added to an acidic silica sol, the molar ratio of Al to Si is controlled at 0.1-0.5, and the mixture is heated to 50-85℃ and kept at this temperature to obtain a small-particle-size silica sol.

5. The production method according to claim 1 or 4, characterized by, The aluminum salt solution is an aluminum sulfate solution.

6. The method of claim 1, wherein, The method for preparing the silicic acid solution includes: An acid solution is added to the cation exchange resin, and after activation, the cation exchange resin is rinsed with deionized water to obtain an acidic cation exchange resin. Water glass is added to an acidic cation exchange resin, and a silicic acid solution is obtained by the reaction.

7. The preparation method according to claim 6, characterized in that, The acid solution is dilute sulfuric acid and / or dilute hydrochloric acid.

8. A small-particle-size silica sol, characterized in that, The small-particle-size silica sol is prepared by the preparation method according to any one of claims 1-7.

9. The small-particle-size silica sol according to claim 8, characterized in that, The particle size of the small-particle silica sol is 4-6 nm.

10. The use of the small-particle-size silica sol according to claim 8 or 9 in the preparation of targeted drug carriers, catalytic reaction carriers or chip packaging and dielectric materials.

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