Stable acidic silica sol and preparation method thereof

Abstract

The invention discloses stable acidic silica sol and a preparation method thereof. The silanol-based blocking agent, the pH stabilizer and the ion chelating agent are mixed with the silica sol, so that the stability of an acidic silica sol system is improved, the conductivity of the system is reduced, the pH is stable, the contact opportunity of colloidal particles is reduced, the colloidal stability is greatly improved, and the colloidal particles can be stabilized for more than 30 days at 60 DEG C when the concentration of the silica sol is more than 30%.

Description

Technical Field

[0001] The invention belongs to the field of silicon dioxide nanomaterials, and particularly relates to a stable acidic silica sol and a preparation method thereof. Background Art

[0002] Silica sol is a colloidal solution formed by the uniform diffusion of silica colloidal particles in water. It is a nanomaterial with excellent performance, odorless, safe and environmentally friendly, and has a wide range of uses, such as precision casting, electronics industry, textile industry, catalysis, coatings, papermaking, food, water treatment, agricultural fertilizers and other civil and military fields. Silica sol has colloidal properties. Zeta potential, Brownian motion and sufficient solvent barrier are the main factors for its stability. Once gelled, it is impossible to disperse and stabilize again, and it is an irreversible colloid. Experience shows that silica sol is stable in the pH range of 2-4 and above pH10. The former is acidic silica sol and the latter is alkaline silica sol. Alkaline silica sol has a high pH and is easy to stabilize. The stability time can be more than 2 years. Acidic silica sol is in a metastable state, and the colloidal particles are easy to condense into gel. It must be stabilized. Obtaining acidic silica sol with a higher concentration (more than 30%) and a longer stability time (more than 6 months) is a technical problem faced by China. Summary of the invention

[0003] The primary purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing a stable acidic silica sol.

[0004] Another object of the present invention is to provide a stable acidic silica sol obtained by the above preparation method.

[0005] Another object of the present invention is to provide an application of the above-mentioned stable acidic silica sol.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a stable acidic silica sol comprises the following steps:

[0008] (1) Preparation of a stabilizer solution: mixing a silanol-based barrier agent, a pH stabilizer, and an ion chelating agent to obtain a stabilizer solution;

[0009] (2) The silica sol and the stabilizer solution are mixed evenly to obtain a stable acidic silica sol.

[0010] The silanol blocking agent described in step (1) is a substance that can block the condensation between silanol groups and play a role in sealing the silanol groups; preferably, it is a hydroxyl-containing compound; more preferably, it is polyethylene glycol 200, glycerol, trimethylolethane, sorbitol, xylitol, glucose, mannitol, methanol, ethanol, isopropanol, hydrolyzed Al 3+ and hydrolyzed Fe 3+At least one of them. The surface of silica sol particles is rich in silanol groups. The finer the particles, the greater the number. The silanol groups are close to each other and condensed, which is the main reason for silica sol gel. The use of hydroxyl-containing compounds can condense silanol groups, block the condensation between silanol groups, and play a role in sealing silanol groups.

[0011] The pH stabilizer in step (1) is a pH regulating acid and an acidic pH buffer. The silica sol particles are hydrolyzed in an acidic system to form silicate molecules, H + As the ion concentration decreases and the pH increases, the silica sol particles automatically polymerize and gel. Use pH adjusting acid to adjust the pH to acidic, increase the system H + The concentration is adjusted by adding an acidic pH buffer to stabilize the pH of the system and prevent the silica sol particles from approaching, thereby achieving a stabilizing colloid effect. The pH adjusting acid is preferably at least one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, phosphoric acid, malic acid, citric acid, tartaric acid, fumaric acid, ascorbic acid, lactic acid and gluconic acid. The acidic pH buffer is preferably at least one of an acetic acid and sodium acetate buffer system, a borax and hydrochloric acid buffer system, a sodium (potassium) dihydrogen phosphate and disodium hydrogen phosphate buffer system, a citric acid-sodium hydroxide-hydrochloric acid buffer buffer system, a citric acid and sodium (ammonium) citrate buffer system, a glycine and hydrochloric acid buffer system, and a tris(hydroxymethyl)aminomethane and hydrochloric acid buffer system.

[0012] The amount of the pH stabilizer is preferably such that the pH of the acidic silica sol is 2 to 4; more preferably such that the pH of the acidic silica sol is 2.7 to 2.9.

[0013] The concentration of the pH stabilizer in step (1) is preferably 1-20% by mass, and more preferably 10% by mass.

[0014] The ion chelating agent described in step (1) is used to reduce the ion concentration and conductivity of the system. This is because the acidic silica sol colloidal particles are very unstable, have high ionicity, high conductivity, strong attraction between the colloidal particles, and are easy to gel. The ion chelating agent is preferably at least one of ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), N-hydroxyethylethylaminetriacetic acid (HEDTA) and ethylene glycol-bis-(B-aminoethyl ether)-N,N-tetraacetic acid (EGTA), sodium tripolyphosphate, sodium polyphosphate, sodium hexametaphosphate, sodium pyrophosphate, polyacrylic acid and maleic acid.

[0015] The concentration of the ion chelating agent in step (1) is preferably 5-20% by mass, and more preferably 10% by mass.

[0016] The mixing conditions in step (1) are preferably stirring at 200-500 rpm for 1-3 h; more preferably stirring at 300 rpm for 2 h.

[0017] The mixing conditions in step (2) are preferably stirring at 200-500 rpm for 0.5-2 h; more preferably stirring at 300 rpm for 1 h.

[0018] In the stable acidic silica sol described in step (2), the amount of each substance used is calculated by mass percentage, based on the solid mass of the silica sol (i.e., the solid mass of the silica sol is used as the denominator), as follows: 5-5.5% of silanol-based barrier agent, 1-1.3% of pH stabilizer, and 0.1-0.15% of ion chelating agent.

[0019] The acidity described in step (2) refers to pH 2-4.

[0020] The solvent used in the present invention is preferably deionized water.

[0021] A stable acidic silica sol is obtained by the above preparation method; wherein the concentration of the silica sol is more than 30% by mass, the pH is 2-4, and it can be stable for more than 30 days at 60°C; preferably: the concentration of the silica sol is 30-31% by mass, the pH is 2.7-2.9, and it can be stable for 35-60 days at 60°C. Stability at 60°C for 30 days is equivalent to stability at room temperature for more than 6 months.

[0022] Compared with the prior art, the present invention has the following advantages and effects:

[0023] The present invention utilizes the triple colloid stabilization technology of hydroxyl stabilization, pH stabilization and ion chelation to improve the stability of the acidic silica sol system, thereby reducing the conductivity of the system, stabilizing the pH, reducing the contact opportunities of the colloid particles, and greatly improving the colloid stability. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0025] The raw material silica sol used in the present invention is acidic silica sol, which is prepared by ion exchange method and has a concentration of more than 30% (the acidic silica sol sample prepared by ion exchange is provided by Foshan Kening New Material Technology Co., Ltd., with a concentration of 34%, 27.6Be, pH 2.27, and a density of 1.24).

[0026] Example 1

[0027] (1) Preparation of stabilizer:

[0028] A. Selection of silanol-based barrier agents: polyethylene glycol 200, methanol, ethanol;

[0029] B. Preparation of pH stabilizer: dilute glacial acetic acid with water to obtain an acetic acid solution with a concentration of 10% by mass; acidic pH buffer citric acid-sodium hydroxide-hydrochloric acid buffer, in which the concentration of citrate is 0.1 mol / L, Na + The concentration is 0.01mol / L, pH3.

[0030] C. Preparation of ion chelating agent: Dissolve ethylenediaminetetraacetic acid (EDTA) and sodium hexametaphosphate in deionized water to obtain 10% by mass EDTA solution and sodium hexametaphosphate solution, respectively.

[0031] D. Preparation of the mixed solution: according to the calculated amount of each substance, mix the deionized water, silanol-based barrier agent and pH stabilizer, then add the ion chelating agent and mix, each adding one and mixing for 1 hour, at room temperature, stirring speed 300 rpm.

[0032] (2) Preparation of stable acidic silica sol: Add the stabilizer obtained in step (1) to the silica sol, mix for 1 hour, at room temperature, and stir at a speed of 300 rpm. The amount of each substance used is calculated by mass percentage based on the solid mass of the silica sol, as follows: polyethylene glycol 200 1%, ethanol 1%, methanol 3%, acetic acid 0.5%, acidic pH buffer citric acid-sodium hydroxide-hydrochloric acid buffer pH 3 0.5%, ethylenediaminetetraacetic acid (EDTA) 0.05%, sodium hexametaphosphate 0.1%.

[0033] The prepared silica sol has a concentration of 30.1%, a pH of 2.81, a conductivity of 6.5 mS, and a thermal stability of 60° C. within 35 days.

[0034] Example 2

[0035] (1) Preparation of stabilizer:

[0036] A. Selection of silanol-based barrier agent: dissolve aluminum chloride in deionized water to obtain an aluminum chloride solution with a concentration of 10% by mass; anhydrous ethanol;

[0037] B. Preparation of pH stabilizer: dilute formic acid with water to obtain a formic acid solution with a concentration of 10% by mass; acidic pH buffer borax and hydrochloric acid system (sodium 0.2M), pH 3.

[0038] C. Preparation of ion chelating agent: Sodium hexametaphosphate is dissolved in deionized water to obtain a sodium hexametaphosphate solution with a concentration of 10% by mass.

[0039] D. Preparation of the mixed solution: according to the calculated amount of each substance, mix the deionized water, silanol-based barrier agent and pH stabilizer, then add the ion chelating agent and mix, each adding one and mixing for 1 hour, at room temperature, stirring speed 300 rpm.

[0040] (2) Preparation of stable acidic silica sol: Add the stabilizer obtained in step (1) to the silica sol, mix for 1 hour, at room temperature, and stir at a speed of 300 rpm. The amounts of the substances used are calculated by mass percentage based on the solid mass of the silica sol: 0.5% aluminum chloride, 5% ethanol, 0.8% formic acid, 0.5% acidic pH buffer borax and hydrochloric acid system, and 0.1% sodium hexametaphosphate.

[0041] The prepared silica sol has a concentration of 30.8%, a pH of 2.72, a conductivity of 6.13 mS, and a thermal stability of 60° C. within 40 days.

[0042] Comparative Example 1

[0043] The difference from Example 1 is that deionized water is used to replace the silanol-based barrier to obtain silica sol, wherein the amount of each substance is calculated by mass percentage based on the solid mass of the silica sol, as follows: acetic acid 0.5%, acidic pH buffer citric acid-sodium hydroxide-hydrochloric acid buffer pH3 0.5%, ethylenediaminetetraacetic acid (EDTA) 0.05%, sodium hexametaphosphate 0.1%. Different from Example 1, only no silanol-based barrier is added, and the acidic silica sol obtained has a pH of 2.73, a conductivity of 6.3mS, and a gel after 10 days of heat storage at 60°C.

[0044] Comparative Example 2

[0045] The difference from Example 1 is that deionized water is used to replace the silanol-based barrier and the ion chelating agent to obtain silica sol, wherein the amount of each substance is calculated by mass percentage based on the solid mass of the silica sol as follows: acetic acid 0.5%, acidic pH buffer citric acid-sodium hydroxide-hydrochloric acid buffer pH3 0.5%. Unlike Example 1, no silanol-based barrier and ion chelating agent are added, and the acidic silica sol obtained has a pH of 2.73, a conductivity of 6.6 mS, and a gel after 7 days of heat storage at 60°C.

[0046] Comparative Example 3

[0047] The raw material silica sol was provided by Foshan Kening New Material Technology Co., Ltd., with a concentration of 34%, 27.6Be, pH 2.27, and a density of 1.24. The material gelled after 3 days of heat storage at 60°C and after 7 days of gelation at room temperature.

[0048] Comparative Example 4

[0049] The difference from Example 2 is that deionized water is used to replace the silanol-based barrier to obtain silica sol, wherein the amount of each substance is calculated by mass percentage based on the solid mass of the silica sol, as follows: dilute formic acid with water to obtain a formic acid solution with a concentration of 10% by mass; acidic pH buffer borax and hydrochloric acid system pH 3, the amount is 0.5%, sodium hexametaphosphate 0.1%. Different from Example 2, only no silanol-based barrier is added, the acidic silica sol obtained has a pH of 2.78, a conductivity of 6.3mS, and a gel after 7 days of heat storage at 60°C.

[0050] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a stable acidic silica sol, characterized in that The following steps are involved: (1) Preparation of a stabilizer solution: mixing a silanol-based barrier agent, a pH stabilizer, and an ion chelating agent to obtain a stabilizer solution; (2) mixing the silica sol and the stabilizer solution uniformly to obtain a stable acidic silica sol; The silanol-based barrier agent is a hydroxyl-containing compound; The pH stabilizers are pH adjusting acids and acidic pH buffers.

2. The method for preparing a stable acidic silica sol according to claim 1, characterized in that: The silanol-based barrier agent is polyethylene glycol 200, glycerol, trimethylolethane, sorbitol, xylitol, glucose, mannitol, methanol, ethanol, isopropanol, hydrolyzed Al 3+ and hydrolyzed Fe 3+ At least one of .

3. The method for preparing a stable acidic silica sol according to claim 1, characterized in that: The pH adjusting acid is at least one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, phosphoric acid, malic acid, citric acid, tartaric acid, fumaric acid, ascorbic acid, lactic acid and gluconic acid; The acidic pH buffer is at least one of an acetic acid and sodium acetate buffer system, a borax and hydrochloric acid buffer system, a sodium (potassium) dihydrogen phosphate and disodium hydrogen phosphate buffer system, a citric acid-sodium hydroxide-hydrochloric acid buffer buffer system, a citric acid and sodium (ammonium) citrate buffer system, a glycine and hydrochloric acid buffer system, and a tris (hydroxymethyl)aminomethane and hydrochloric acid buffer system.

4. The method for preparing a stable acidic silica sol according to claim 1, characterized in that: The dosage of the pH stabilizer is such that the pH of the acidic silica sol is 2-4.

5. The method for preparing a stable acidic silica sol according to claim 1, characterized in that: The ion chelating agent described in step (1) is at least one of ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, N-hydroxyethylethylaminetriacetic acid and ethylene glycol-bis-(B-aminoethyl ether)-N,N-tetraacetic acid, sodium tripolyphosphate, sodium polyphosphate, sodium hexametaphosphate, sodium pyrophosphate, polyacrylic acid and maleic acid.

6. The method for preparing a stable acidic silica sol according to claim 1, characterized in that: The mixing conditions described in step (1) are stirring at 200-500 rpm for 1-3 hours; The mixing condition in step (2) is stirring at 200-500 rpm for 0.5-2 h.

7. The method for preparing a stable acidic silica sol according to claim 1, characterized in that: In the stable acidic silica sol described in step (2), the amount of each substance used is calculated by mass percentage based on the solid mass of the silica sol, as follows: 5-5.5% of silanol-based barrier agent, 1-1.3% of pH stabilizer, and 0.1-0.15% of ion chelating agent.

8. A stable acidic silica sol, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 7.

9. The stable acidic silica sol according to claim 8, characterized in that: The concentration of the silica sol is more than 30% by mass, the pH is 2-4, and it can be stable at 60° C. for more than 30 days.